HUMAN GENOME SCIENCES INC
8-K, 1999-12-16
IN VITRO & IN VIVO DIAGNOSTIC SUBSTANCES
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<PAGE>   1
                       SECURITIES AND EXCHANGE COMMISSION

                              WASHINGTON, DC 20549

                             -----------------------

                                    FORM 8-K

                                 CURRENT REPORT
                     PURSUANT TO SECTION 13 OR 15(d) OF THE
                         SECURITIES EXCHANGE ACT OF 1934

                                DECEMBER 13, 1999

                                 Date of Report
                        (Date of earliest event reported)

                           HUMAN GENOME SCIENCES, INC.
                           ---------------------------

               (Exact Name of Registrant as Specified in Charter)

<TABLE>
<S>                                               <C>                           <C>
                     DELAWARE                                0-022962                       22-3178468
  (State or Other Jurisdiction of Incorporation)     (Commission File Number)   (IRS Employer Identification No.)
</TABLE>

              9410 KEY WEST AVENUE, ROCKVILLE, MARYLAND 20850-3338
              ----------------------------------------------------
               (Address of Principal Executive Offices) (ZIP Code)

       Registrant's telephone number, including area code: (301) 309-8504
                                                           --------------

          (Former Name or Former Address, if Changed Since Last Report)


<PAGE>   2


ITEM 5.   OTHER EVENTS.

(a)       COMMENCEMENT OF TENDER OFFER FOR 5 1/2% CONVERTIBLE SUBORDINATED NOTES

          On December 13, 1999, Human Genome Sciences, Inc. (the "Company")
announced that it is offering holders of its existing 5 1/2% Convertible
Subordinated Notes Due 2006 (the "Existing Notes") an inducement to convert
their Existing Notes prior to 5:00 p.m., New York City time, on Wednesday,
January 12, 2000. Holders who tender their Existing Notes for conversion prior
to that time will receive an additional $180 per $1,000 principal amount of
Existing Notes tendered, payable in shares of the Company's common stock, par
value $0.01 per share, based upon the average closing price of the common stock
on the three trading days prior to January 12, 2000. This common stock is in
addition to the 19.1571 shares issuable to holders of the Existing Notes for
each $1,000 principal amount of Existing Notes converted under the terms of the
Existing Notes. The Company will also make a cash payment for accrued interest
from January 1, 2000 and any fractional shares. The Existing Notes were issued
in June and July of 1999 and are convertible into the Company's common stock at
a price of $52.20 per share.

          The exchange offer for the Existing Notes is being made for a limited
time only, and will expire at 5:00 p.m., New York City time, on Wednesday,
January 12, 2000, unless extended by the Company. Individuals who have questions
or who wish to obtain information about the exchange offer may contact the
information agent, Georgeson Shareholder Communications Inc., 17 State Street,
New York, New York 10004, telephone number (800) 223-2064.

(b)       COMPLETION OF SALE OF 5% CONVERTIBLE SUBORDINATED NOTES

          On December 14, 1999, the Company completed the sale of its private
offering of $150,000,000 aggregate principal amount of 5% Convertible
Subordinated Notes Due 2006 (the "New Notes"). The Company will pay interest on
the New Notes on June 15 and December 15 of each year, commencing on June 15,
2000. The New Notes will mature on December 15, 2006.

          The New Notes are convertible at any time prior to maturity into
shares of the Company's common stock at a conversion price of $143.25 per share,
which is equivalent to a conversion rate of 6.9808 shares per $1,000 principal
amount of New Notes and is subject to adjustment under the terms of the New
Notes. The New Notes are subordinated to all of the Company's existing and
future senior indebtedness.

          The Company may redeem the New Notes on or after December 20, 2002.
Prior to that date, the Company may redeem the New Notes if the price of its
common stock has exceeded 150% of the conversion price for at least 20 of the 30
trading days prior to redemption and the Company makes an additional "make
whole" payment on the redeemed New Notes. Holders may require the Company to
repurchase the New Notes upon a Change in Control, except that this repurchase
right does not apply to transactions in which at least 90% of the
<PAGE>   3

consideration consists of common stock and in certain other circumstances under
the terms of the New Notes.

          The Company has agreed to file a shelf registration statement with
respect to the New Notes pursuant to a Registration Rights Agreement dated as of
December 14, 1999. In the event the Company fails to comply with its obligations
under the Registration Rights Agreement, it will pay additional interest on the
New Notes.

(c)       AMENDMENT OF CERTIFICATE OF INCORPORATION

          On December 16, 1999, the stockholders of the Company approved at a
special meeting, and the Company filed with the Delaware Secretary of State, an
amendment to the Company's Restated Certificate of Incorporation (Fifth) which
increased the Company's authorized Common Stock from 50,000,000 to 250,000,000
shares, and increased the Company's authorized Preferred Stock from 1,000,000
to 20,000,000 shares.

ITEM 7.   FINANCIAL STATEMENTS, PRO FORMA FINANCIAL INFORMATION AND EXHIBITS.

          (c)   Exhibits.

          3.1       Amendment to Restated Certificate of Incorporation.

          4.1       Indenture dated as of December 14, 1999 between Human Genome
                    Sciences, Inc. and The Bank of New York, as trustee,
                    including the form of 5% Convertible Subordinated Notes Due
                    2006 included in Article II thereof.

          4.2       Registration Rights Agreement dated as of December 14, 1999
                    between Human Genome Sciences, Inc. and the Initial
                    Purchaser.


                                   SIGNATURES

          Pursuant to the requirements of the Securities Exchange Act of 1934,
the Registrant has duly caused this report to be signed on its behalf by the
undersigned hereunto duly authorized.

                                          HUMAN GENOME SCIENCES, INC.


Date:  December 16, 1999                  By:  /s/ Steven C. Mayer
                                               -------------------
                                               Steven C. Mayer
                                               Senior Vice President and Chief
                                                Financial Officer


<PAGE>   4


                                  EXHIBIT INDEX

<TABLE>
<CAPTION>
Exhibit Number          Description
- --------------          -----------
<S>                   <C>
      3.1               Amendment to Restated Certificate of Incorporation.

      4.1               Indenture dated as of December 14, 1999
                        between Human Genome Sciences, Inc. and The
                        Bank of New York, as trustee, including the
                        form of 5% Convertible Subordinated Notes
                        Due 2006 included in Article II thereof.

      4.2               Registration Rights Agreement dated as of December 14,
                        1999 between Human Genome Sciences, Inc. and the Initial
                        Purchaser.
</TABLE>


<PAGE>   1
                                                                     EXHIBIT 3.1

                            CERTIFICATE OF AMENDMENT
                                       TO
                  RESTATED CERTIFICATE OF INCORPORATION (FIFTH)
                                       OF
                           HUMAN GENOME SCIENCES, INC.

                             Pursuant to Section 242
                         of the General Corporation Law
                            of the State of Delaware
                            ------------------------

      Human Genome Sciences, Inc. (hereinafter called the "Corporation"),
organized and existing under and by virtue of the General Corporation Law of
the State of Delaware, does hereby certify as follows:

      FIRST:  In accordance with the General Corporation Law of the State of
Delaware, the Board of Directors of the Corporation adopted resolutions
pursuant to Section 242 of the General Corporation Law of the State of
Delaware setting forth an amendment to the Restated Certificate of
Incorporation (Fifth) of the Corporation and declaring said amendment to be
advisable.  The stockholders of the Corporation duly approved said proposed
amendment at a special meeting in accordance with Section 211 of the General
Corporation Law of the State of Delaware.  The resolutions setting forth the
amendment are as follows:

      RESOLVED:  That Article III(a) of the Restated Certificate of
Incorporation (Fifth) be and hereby is amended by deleting the existing
Article III(a) and inserting the following paragraph in lieu thereof:

      "(a)  Authorization.  The total number of shares of all classes
      of stock which the Corporation shall have authority to issue is
      270,000,000 shares, consisting of 20,000,000 shares of Preferred
      Stock, par value $.01 per share (the "Preferred Stock"), and
      250,000,000 shares of Common Stock, par value $.01 per share
      (the "Common Stock")."

      RESOLVED:  That Article III(c)(1) of the Restated Certificate of
Incorporation (Fifth) be and hereby is amended by deleting the existing
Article III(c)(1) and inserting the following paragraph in lieu thereof:

      "(1)  Designation and Amount.  The designation of this class of
      capital stock shall be Common Stock, par value $.01 per share
      ("Common Stock").  The number of shares, powers, terms,
      conditions, designations, preferences and privileges, relative,
      participating, optional and other special rights, and
      qualifications, limitations and restrictions, shall be as set
      forth in this Article III(c).  The number of authorized shares
      of Common Stock is 250,000,000.  The number of authorized shares
      of Common Stock may be increased or decreased

<PAGE>   2
      (but not below the number of shares thereof then outstanding) by the
      affirmative vote of the holders of the majority of the stock of the
      Corporation entitled to vote, irrespective of the provisions of section
      242(b)(2) of the Delaware General Corporation Law."

      IN WITNESS WHEREOF, the Corporation has caused its corporate seal to be
affixed hereto and this Certificate of Amendment to be signed by its Chairman
of the Board and Chief Executive Officer this 16th day of December, 1999.

[Corporate Seal]              HUMAN GENOME SCIENCES, INC.



                              By: /s/ William A. Haseltine
                                  ----------------------------
                              William A. Haseltine, Ph.D.
                              Chairman of the Board and Chief Executive
                              Officer



                                     - 2 -




<PAGE>   1
                                                                     EXHIBIT 4.1


                                                                  EXECUTION COPY
================================================================================





                                   INDENTURE


                          HUMAN GENOME SCIENCES, INC.


                                       to


                              THE BANK OF NEW YORK

                                    Trustee





                   5% Convertible Subordinated Notes Due 2006



                         Dated as of December 14, 1999





================================================================================
<PAGE>   2



                               Table of Contents

<TABLE>
<CAPTION>
                                                                                                  Page
                                                                                                  ----


                                                              ARTICLE I

                                       Definitions and Other Provisions of General Application
                                       -------------------------------------------------------

<S>              <C>                                                                              <C>
SECTION 1.01.    Definitions  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .    1
SECTION 1.02.    Compliance Certificates and Opinions . . . . . . . . . . . . . . . . . . . . . .    9
SECTION 1.03.    Form of Documents Delivered to Trustee . . . . . . . . . . . . . . . . . . . . .   10
SECTION 1.04.    Acts of Holders: Record Dates  . . . . . . . . . . . . . . . . . . . . . . . . .   10
SECTION 1.05.    Notices, etc., to Trustee and Company  . . . . . . . . . . . . . . . . . . . . .   12
SECTION 1.06.    Notice to Holders: Waiver  . . . . . . . . . . . . . . . . . . . . . . . . . . .   12
SECTION 1.07.    Conflict with Trust Indenture Act  . . . . . . . . . . . . . . . . . . . . . . .   13
SECTION 1.08.    Effect of Headings and Table of Contents . . . . . . . . . . . . . . . . . . . .   13
SECTION 1.09.    Successors and Assigns . . . . . . . . . . . . . . . . . . . . . . . . . . . . .   13
SECTION 1.10.    Severability Clause  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .   13
SECTION 1.11.    Benefits of Indenture  . . . . . . . . . . . . . . . . . . . . . . . . . . . . .   13
SECTION 1.12.    Governing Law  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .   13
SECTION 1.13.    Legal Holidays . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .   13


                                                              ARTICLE II

                                                            Security Forms
                                                            --------------

SECTION 2.01.    Forms Generally  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .   14
SECTION 2.02.    Form of Face of Security . . . . . . . . . . . . . . . . . . . . . . . . . . . .   15
SECTION 2.03.    Form of Reverse of Security  . . . . . . . . . . . . . . . . . . . . . . . . . .   18
SECTION 2.04.    Form of Trustee's Certificate of Authentication  . . . . . . . . . . . . . . . .   22
SECTION 2.05.    Form of Conversion Notice  . . . . . . . . . . . . . . . . . . . . . . . . . . .   23
SECTION 2.06.    Form of Certification  . . . . . . . . . . . . . . . . . . . . . . . . . . . . .   24


                                                             ARTICLE III

                                                            The Securities
                                                            --------------

SECTION 3.01.    Title and Terms  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .   25
SECTION 3.02.    Denominations  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .   25
SECTION 3.03.    Execution, Authentication, Delivery and Dating . . . . . . . . . . . . . . . . .   25
SECTION 3.04.    Global and Non-Global Securities . . . . . . . . . . . . . . . . . . . . . . . .   26
SECTION 3.05.    Registration; Registration of Transfer and Exchange  . . . . . . . . . . . . . .   27
SECTION 3.06.    Mutilated, Destroyed, Lost and Stolen Securities . . . . . . . . . . . . . . . .   31
SECTION 3.07.    Payment of Interest; Interest Rights Preserved   . . . . . . . . . . . . . . . .   31
SECTION 3.08.    Persons Deemed Owners  . . . . . . . . . . . . . . . . . . . . . . . . . . . . .   33
SECTION 3.09.    Cancellation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .   33
SECTION 3.10.    Computation of Interest  . . . . . . . . . . . . . . . . . . . . . . . . . . . .   33
</TABLE>


                                     -ii-
<PAGE>   3

<TABLE>
<CAPTION>
                                                                                                  Page
                                                                                                  ----


                                                              ARTICLE IV

                                                      Satisfaction and Discharge
                                                      --------------------------

<S>              <C>                                                                              <C>
SECTION 4.01.    Satisfaction and Discharge of Indenture  . . . . . . . . . . . . . . . . . . . .   33
SECTION 4.02.    Application of Trust Money . . . . . . . . . . . . . . . . . . . . . . . . . . .   34


                                                              ARTICLE V

                                                               Remedies
                                                               --------

SECTION 5.01.    Events of Default  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .   35
SECTION 5.02.    Acceleration of Maturity; Rescission and Annulment . . . . . . . . . . . . . . .   36
SECTION 5.03.    Collection of Indebtedness and Suits for Enforcement
                   by Trustee . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .   37
SECTION 5.04.    Trustee May File Proofs of Claim . . . . . . . . . . . . . . . . . . . . . . . .   38
SECTION 5.05.    Trustee May Enforce Claims Without Possession of
                   Securities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .   39
SECTION 5.06.    Application of Money Collected . . . . . . . . . . . . . . . . . . . . . . . . .   39
SECTION 5.07.    Limitation on Suits  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .   39
SECTION 5.08.    Unconditional Right of Holders to Receive Principal,
                   Premium and Interest and To Convert  . . . . . . . . . . . . . . . . . . . . .   40
SECTION 5.09.    Restoration of Rights and Remedies . . . . . . . . . . . . . . . . . . . . . . .   40
SECTION 5.10.    Rights and Remedies Cumulative . . . . . . . . . . . . . . . . . . . . . . . . .   40
SECTION 5.11.    Delay or Omission Not Waiver . . . . . . . . . . . . . . . . . . . . . . . . . .   40
SECTION 5.12.    Control by Holders . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .   40
SECTION 5.13.    Waiver of Past Defaults  . . . . . . . . . . . . . . . . . . . . . . . . . . . .   41
SECTION 5.14.    Undertaking for Costs  . . . . . . . . . . . . . . . . . . . . . . . . . . . . .   41
SECTION 5.15.    Waiver of Usury, Stay or Extension Laws  . . . . . . . . . . . . . . . . . . . .   41


                                                              ARTICLE VI

                                                             The Trustee
                                                             -----------

SECTION 6.01.    Certain Duties and Responsibilities  . . . . . . . . . . . . . . . . . . . . . .   42
SECTION 6.02.    Notice of Defaults . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .   43
SECTION 6.03.    Certain Rights of Trustee  . . . . . . . . . . . . . . . . . . . . . . . . . . .   43
SECTION 6.04.    Not Responsible for Recitals or Issuance of Securities . . . . . . . . . . . . .   44
SECTION 6.05.    May Hold Securities  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .   44
SECTION 6.06.    Money Held in Trust  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .   44
SECTION 6.07.    Compensation and Reimbursement . . . . . . . . . . . . . . . . . . . . . . . . .   44
SECTION 6.08.    Disqualification; Conflicting Interests  . . . . . . . . . . . . . . . . . . . .   45
SECTION 6.09.    Corporate Trustee Required; Eligibility  . . . . . . . . . . . . . . . . . . . .   45
SECTION 6.10.    Resignation and Removal; Appointment of Successor  . . . . . . . . . . . . . . .   45
SECTION 6.11.    Acceptance of Appointment by Successor . . . . . . . . . . . . . . . . . . . . .   46
SECTION 6.12.    Merger, Conversion, Consolidation or Succession
                   to Business  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .   47
SECTION 6.13.    Preferential Collection of Claims Against Company  . . . . . . . . . . . . . . .   47
</TABLE>





                                    -iii-
<PAGE>   4

<TABLE>
<CAPTION>
                                                                                                  Page
                                                                                                  ----


<S>              <C>                                                                               <C>
SECTION 6.14.    Appointment of Authenticating Agent  . . . . . . . . . . . . . . . . . . . . . .   47
SECTION 6.15.    Appointment of Co-Trustee  . . . . . . . . . . . . . . . . . . . . . . . . . . .   48


                                                             ARTICLE VII

                                          Holders' Lists and Reports by Trustee and Company
                                          -------------------------------------------------

SECTION 7.01.    Company to Furnish Trustee Names and Addresses
                   of Holders   . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .   49
SECTION 7.02.    Preservation of Information; Communications to
                   Holders  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .   49
SECTION 7.03.    Reports by Trustee   . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .   50
SECTION 7.04.    Reports by Company . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .   50


                                                             ARTICLE VIII

                                         Consolidation, Merger, Conveyance, Transfer or Lease
                                         ----------------------------------------------------

SECTION 8.01.    Company May Consolidate, etc., Only on Certain Terms . . . . . . . . . . . . . .   50
SECTION 8.02.    Successor Substituted  . . . . . . . . . . . . . . . . . . . . . . . . . . . . .   51


                                                              ARTICLE IX

                                                       Supplemental Indentures
                                                       -----------------------

SECTION 9.01.    Supplemental Indentures Without Consent of Holders . . . . . . . . . . . . . . .   51
SECTION 9.02.    Supplemental Indentures with Consent of Holders  . . . . . . . . . . . . . . . .   52
SECTION 9.03.    Execution of Supplemental Indentures . . . . . . . . . . . . . . . . . . . . .     53
SECTION 9.04.    Effect of Supplemental Indentures  . . . . . . . . . . . . . . . . . . . . . . .   53
SECTION 9.05.    Conformity with Trust Indenture Act  . . . . . . . . . . . . . . . . . . . . . .   53
SECTION 9.06.    Reference in Securities to Supplemental Indentures . . . . . . . . . . . . . . .   53

                                                              ARTICLE X

                                                              Covenants
                                                              ---------

SECTION 10.01.   Payment of Principal, Premium and Interest . . . . . . . . . . . . . . . . . . .   54
SECTION 10.02.   Maintenance of Office or Agency  . . . . . . . . . . . . . . . . . . . . . . . .   54
SECTION 10.03.   Money for Security Payments To Be Held in Trust  . . . . . . . . . . . . . . . .   54
SECTION 10.04.   Statement by Officers as to Default  . . . . . . . . . . . . . . . . . . . . . .   55
SECTION 10.05.   Existence  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .   56
SECTION 10.06.   Maintenance of Properties  . . . . . . . . . . . . . . . . . . . . . . . . . . .   56
SECTION 10.07.   Payment of Taxes and Other Claims  . . . . . . . . . . . . . . . . . . . . . . .   56
SECTION 10.08.   Waiver of Certain Covenants  . . . . . . . . . . . . . . . . . . . . . . . . . .   56
SECTION 10.09.   Delivery of Certain Information  . . . . . . . . . . . . . . . . . . . . . . . .   56
SECTION 10.10.   Resale of Certain Securities; Reporting Issuer . . . . . . . . . . . . . . . . .   57
</TABLE>





                                     -iv-
<PAGE>   5

<TABLE>
<CAPTION>
                                                                                                  Page
                                                                                                  ----


<S>              <C>                                                                              <C>
SECTION 10.11.   Registration Rights  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .   57


                                                              ARTICLE XI

                                                       Redemption of Securities
                                                       ------------------------

SECTION 11.01.   Right of Provisional Redemption  . . . . . . . . . . . . . . . . . . . . . . . .   58
SECTION 11.02.   Right of Optional Redemption . . . . . . . . . . . . . . . . . . . . . . . . . .   59
SECTION 11.03.   Applicability of Article . . . . . . . . . . . . . . . . . . . . . . . . . . . .   59
SECTION 11.04.   Election to Redeem; Notice to Trustee  . . . . . . . . . . . . . . . . . . . . .   59
SECTION 11.05.   Selection by Trustee of Securities to Be Redeemed  . . . . . . . . . . . . . . .   59
SECTION 11.06.   Notice of Redemption . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .   60
SECTION 11.07.   Deposit of Redemption Price  . . . . . . . . . . . . . . . . . . . . . . . . . .   60
SECTION 11.08.   Securities Payable on Redemption Date  . . . . . . . . . . . . . . . . . . . . .   61
SECTION 11.09.   Securities Redeemed in Part  . . . . . . . . . . . . . . . . . . . . . . . . . .   62
SECTION 11.10.   Conversion Arrangement on Call for Redemption. . . . . . . . . . . . . . . . . .   62


                                                             ARTICLE XII

                                                     Subordination of Securities
                                                     ---------------------------

SECTION 12.01.   Securities Subordinate to Senior Indebtedness  . . . . . . . . . . . . . . . . .   63
SECTION 12.02.   Payment over of Proceeds upon Dissolution, Etc.  . . . . . . . . . . . . . . . .   63
SECTION 12.03.   No Payment When Senior Indebtedness in Default . . . . . . . . . . . . . . . . .   64
SECTION 12.04.   Payment Permitted If No Default  . . . . . . . . . . . . . . . . . . . . . . . .   64
SECTION 12.05.   Subrogation to Rights of Holders of Senior Indebtedness  . . . . . . . . . . . .   64
SECTION 12.06.   Provisions Solely to Define Relative Rights  . . . . . . . . . . . . . . . . . .   65
SECTION 12.07.   Trustee to Effectuate Subordination  . . . . . . . . . . . . . . . . . . . . . .   65
SECTION 12.08.   No Waiver of Subordination Provisions  . . . . . . . . . . . . . . . . . . . . .   65
SECTION 12.09.   Notice to Trustee  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .   66
SECTION 12.10.   Reliance on Judicial Order or Certificate of
                   Liquidating Agent  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .   67
SECTION 12.11.   Trustee Not Fiduciary for Holders of Senior Indebtedness . . . . . . . . . . . .   67
SECTION 12.12.   Rights of Trustee as Holder of Senior Indebtedness;
                   Preservation of Trustee's Rights . . . . . . . . . . . . . . . . . . . . . . .   67
SECTION 12.13.   Article Applicable to Paying Agents  . . . . . . . . . . . . . . . . . . . . . .   67
SECTION 12.14.   Certain Conversions Deemed Payment . . . . . . . . . . . . . . . . . . . . . . .   67


                                                             ARTICLE XIII

                                                       Conversion of Securities
                                                       ------------------------

SECTION 13.01.   Conversion Privilege and Conversion Price  . . . . . . . . . . . . . . . . . . .   68
SECTION 13.02.   Exercise of Conversion Privilege . . . . . . . . . . . . . . . . . . . . . . . .   69
SECTION 13.03.   Fractions of Shares  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .   70
SECTION 13.04.   Adjustment of Conversion Price . . . . . . . . . . . . . . . . . . . . . . . . .   70
SECTION 13.05.   Notice of Adjustments of Conversion Price  . . . . . . . . . . . . . . . . . . .   75
SECTION 13.06.   Notice of Certain Corporate Action . . . . . . . . . . . . . . . . . . . . . . .   75
</TABLE>



                                      -v-

<PAGE>   6

<TABLE>
<CAPTION>
                                                                                                  Page
                                                                                                  ----


<S>              <C>                                                                              <C>
SECTION 13.07.   Company to Reserve Common Stock  . . . . . . . . . . . . . . . . . . . . . . . .   76
SECTION 13.08.   Taxes on Conversions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .   76
SECTION 13.09.   Covenant as to Common Stock  . . . . . . . . . . . . . . . . . . . . . . . . . .   76
SECTION 13.10.   Cancellation of Converted Securities . . . . . . . . . . . . . . . . . . . . . .   77
SECTION 13.11.   Provisions in Case of Reclassification, Consolidation,
                   Merger or Sale of Assets . . . . . . . . . . . . . . . . . . . . . . . . . . .   77


                                                             ARTICLE XIV

                                                     Right to Require Repurchase
                                                     ---------------------------

SECTION 14.01.   Right to Require Repurchase  . . . . . . . . . . . . . . . . . . . . . . . . . .   77
SECTION 14.02.   Notice, Method of Exercising Repurchase Right  . . . . . . . . . . . . . . . . .   77
SECTION 14.03.   Deposit of Repurchase Price  . . . . . . . . . . . . . . . . . . . . . . . . . .   78
SECTION 14.04.   Securities Not Repurchased on Repurchase Date  . . . . . . . . . . . . . . . . .   78
SECTION 14.05.   Securities Repurchased in Part . . . . . . . . . . . . . . . . . . . . . . . . .   79
SECTION 14.06.   Certain Definitions  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .   79

                                                              ARTICLE XV

                                                  Defeasance and Covenant Defeasance
                                                  ----------------------------------

SECTION 15.01.   Company's Option to Effect Defeasance or Covenant
                   Defeasance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .   80
SECTION 15.02.   Defeasance and Discharge . . . . . . . . . . . . . . . . . . . . . . . . . . . .   80
SECTION 15.03.   Covenant Defeasance  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .   81
SECTION 15.04.   Conditions to Defeasance or Covenant Defeasance  . . . . . . . . . . . . . . . .   81
SECTION 15.05.   Deposited Money and U.S. Government Obligations
                   to Be Held in Trust; Other Miscellaneous Provisions  . . . . . . . . . . . . .   83
SECTION 15.06.   Reinstatement  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .   83


                                                             ARTICLE XVI

                                                               Immunity
                                                               --------

SECTION 16.01.   Personal Immunity of Incorporators, Shareholders,
                   Directors and Officers . . . . . . . . . . . . . . . . . . . . . . . . . . . .   84
</TABLE>



                                     -vi-
<PAGE>   7


                                        INDENTURE dated as of December 14, 1999,
                              between HUMAN GENOME SCIENCES, INC., a corporation
                              duly organized and existing under the laws of the
                              State of Delaware (herein called the "Company"),
                              having its principal office at 9410 Key West
                              Avenue, Rockville, Maryland 20850-3338, and THE
                              BANK OF NEW YORK, as Trustee (herein called the
                              "Trustee").


                 The Company has duly authorized the execution and delivery of
this Indenture to provide for the issuance of its 5% Convertible Subordinated
Notes due 2006 (herein called the "Securities"), to be issued as in this
Indenture provided.

                 All things necessary to make the Securities, when executed by
the Company and authenticated and delivered hereunder and duly issued by the
Company, the valid obligations of the Company, and to make this Indenture a
valid agreement of the Company, in accordance with their and its terms, have
been done.


                             W I T N E S S E T H :

                 For and in consideration of the premises and the purchase of
the Securities by the Holders thereof, it is mutually agreed, for the equal and
proportionate benefit of all Holders of the Securities or of any series
thereof, as follows:


                                   ARTICLE I

            Definitions and Other Provisions of General Application

                 SECTION 1.01.  Definitions.  For all purposes of this
Indenture, except as otherwise expressly provided or unless the context
otherwise requires:

                 1.  The terms defined in this Article have the meanings
assigned to them in this Article and include the plural as well as the
singular.

                 2.  All other terms used herein which are defined in the Trust
Indenture Act, either directly or by reference therein, have the meanings
assigned to them therein.

                 3.  All accounting terms not otherwise defined herein have the
meanings assigned to them in accordance with generally accepted accounting
principles, and, except as otherwise herein expressly provided, the term
"generally accepted accounting principles" with respect to any computation
required or permitted hereunder shall mean such accounting principles as are
generally accepted at the date of such computation.

                 4.  Unless the context otherwise requires, any reference to an
"Article" or a "Section" refers to an Article or Section, as the case may be,
of this Indenture.

                 5.  The words "herein", "hereof and "hereunder" and other
words of similar import refer to this Indenture as a whole and not to any
particular Article, Section or other subdivision.
<PAGE>   8
                                                                               2




                 Certain terms used in Article XIV have the meanings specified
therein.

                 "Act", when used with respect to any Holder, has the meaning
specified in Section 1.04.

                 "Additional Interest" has the meaning specified in Section
10.11.

                 "Affiliate" of any specified Person means any other Person who
directly, or indirectly through one or more intermediaries, controls, is
controlled by, or is under common control with, such specified Person.  For the
purposes of this definition, "control" when used with respect to any specified
Person means the power to direct the management and policies of such Person,
directly or indirectly, whether through the ownership of voting securities, by
contract or otherwise; and the terms "controlling" and "controlled" have
meanings correlative to the foregoing.

                 "Agent Member" means any member of, or participant in, the
Depositary.

                 "Applicable Procedures" means, with respect to any transfer or
transaction involving a Global Security or beneficial interest therein, the
rules and procedures of the Depositary for such Security, in each case to the
extent applicable to such transaction and as in effect from time to time.

                 "Authenticating Agent" means any Person authorized by the
Trustee pursuant to Section 6.14 to act on behalf of the Trustee to
authenticate Securities.

                 "Beneficial Owner" has the meaning specified in Section 14.06.

                 "Board of Directors" means either the board of directors of
the Company or any duly authorized committee of that board.

                 "Board Resolution" means a copy of a resolution certified by
the Secretary or an Assistant Secretary of the Company to have been duly
adopted by the Board of Directors and to be in full force and effect on the
date of such certification, and delivered to the Trustee.

                 "Business Day" means a day on which banking institutions are
open for business and carrying out transactions in Dollars at the relevant
place of payment.

                 "Change in Control" has the meaning specified in Section
14.06.

                 "Closing Price" on any Trading Day with respect to the per
share price of Common Stock means the last reported sales price regular way or,
in case no such reported sale takes place on such Trading Day, the average of
the reported closing bid and asked prices regular way, in either case on the
New York Stock Exchange or, if the Common Stock is not listed or admitted to
trading on the New York Stock Exchange, on the principal national securities
exchange on which the Common Stock is listed or admitted to trading, or, if not
listed or admitted to trading on any national securities exchange, on The
Nasdaq Stock Market, Inc.  ("Nasdaq") or, if the Common Stock is not listed or
admitted to trading on any national securities exchange or Nasdaq, the average
of the closing bid and asked prices in the over-the-counter market as furnished
by any New
<PAGE>   9
                                                                               3


York Stock Exchange member firm that is selected from time to time by the
Company for that purpose and is reasonably acceptable to the Trustee.

                 "Commencement Date" has the meaning specified in Section
13.04.

                 "Commission" means the Securities and Exchange Commission, as
from time to time constituted, created under the Exchange Act, or, if at any
time after the execution of this instrument such Commission is not existing and
performing the duties now assigned to it under the Trust Indenture Act, then
the body performing such duties at such time.

                 "Common Stock" includes any stock of any class of the Company
which has no preference in respect of dividends or of amounts payable in the
event of any voluntary or involuntary liquidation, dissolution or winding-up of
the Company and which is not subject to redemption by the Company.  However,
subject to the provisions of Section 13.11, shares issuable on conversion of
Securities shall include only shares of the class designated as Common Stock of
the Company at the date of this instrument or shares of any class or classes
resulting from any reclassification or reclassifications thereof and which have
no preference in respect of dividends or of amounts payable in the event of any
voluntary or involuntary liquidation, dissolution or winding-up of the Company
and which are not subject to redemption by the Company; provided that if at any
time there shall be more than one such resulting class, the shares of each such
class then so issuable shall be substantially in the proportion which the total
number of shares of such class resulting from all such reclassifications bears
to the total number of shares of all such classes resulting from all such
reclassifications.

                 "Company" means the Person named as the "Company" in the first
paragraph of this instrument until a successor Person shall have become such
pursuant to the applicable provisions of this Indenture, and thereafter
"Company" shall mean such successor Person.

                 "Company Order" has the meaning specified in the definition of
Company Request in this Section 1.01.

                 "Company Request" or "Company Order" means a written request
or order signed in the name of the Company by its Chairman of the Board, its
Vice Chairman of the Board, its President or a Vice President, and by its
Treasurer, an Assistant Treasurer, its Secretary or an Assistant Secretary, and
delivered to the Trustee.

                 "Corporate Trust Office" means the principal office of the
Trustee in the city at which at any particular time its corporate trust
business shall be administered.  As of the date hereof, the Corporate Trust
Office of the Trustee is located at 101 Barclay Street, Floor 21 West, New
York, New York 10286.

                 "Corporation" means a corporation, association, company,
joint-stock company or business trust.

                 "Current Event" has the meaning specified in Section 13.04.

                 "Defaulted Interest" has the meaning specified in Section
3.07.
<PAGE>   10
                                                                               4




                 "Depositary" means, with respect to the Securities issued in
whole or in part in the form of one or more Global Securities, a clearing
agency registered under the Exchange Act that is designated to act as
Depositary for such Securities as contemplated by Section 2.01 (or any
successor securities clearing agency so registered).

                 "Distribution Date" has the meaning specified in Section
13.04.

                 "Dollar" or "U.S.$" means a Dollar or other equivalent unit in
such coin or currency of the United States as at the time shall be legal tender
for the payment of public and private debts.

                 "DTC" means The Depository Trust Company, a New York
corporation.

                 "Event of Default" has the meaning specified in Section 5.01.

                 "ex date" has the meaning specified in Section 13.04.

                 "Exchange Act" means the Securities Exchange Act of 1934 as it
may be amended from time to time, and any successor act thereto, and the rules
and regulations of the Commission promulgated thereunder.

                 "Expiration Date" has the meaning specified in Section 1.04.

                 "Expiration Time" has the meaning specified in Section 13.04.

                 "Global Security" means a Security that is registered in the
Security Register in the name of a Depositary or a nominee thereof.

                 "Group" has the meaning specified in Section 14.06.

                 "Holder" means a Person in whose name a Security is registered
in the Security Register.

                 "Indenture" means this instrument as originally executed or as
it may from time to time be supplemented or amended by one or more indentures
supplemental hereto entered into pursuant to the applicable provisions hereof,
including, for all purposes of this instrument and any such supplemental
indenture, the provisions of the Trust Indenture Act that are deemed to be a
part of and govern this instrument and any such supplemental indenture,
respectively.

                 "Initial Purchaser" means Credit Suisse First Boston
Corporation.

                 "Interest Payment Date" means the Stated Maturity of an
installment of interest on the Securities.

                 "Issue Date" means the date of first issuance of the
Securities under this Indenture.

                 "junior securities" has the meaning specified in Section
12.14.
<PAGE>   11
                                                                               5




                 "Make-Whole Payment" has the meaning specified in Section
11.01.

                 "Maturity", when used with respect to any Security, means the
date on which the principal of such Security or an installment of principal
becomes due and payable as therein or herein provided, whether at the Stated
Maturity or by declaration of acceleration, call for redemption, exercise of
the repurchase right or otherwise.

                 "Nasdaq" has the meaning specified in the definition of Closing
Price in this Section 1.01.

                 "Non-Recourse Obligation" means indebtedness or other
obligation or that portion of indebtedness or other obligation incurred by a
Subsidiary (the "Non-Recourse Subsidiary") with respect to the acquisition of
assets not previously owned by the Company or any Subsidiary or the financing
of a project involving the development or expansion of properties of the
Company or any Subsidiary (i) as to which neither the Company nor any of its
Subsidiaries (other than the Non-Recourse Subsidiary) (a) provides credit
support (including any undertaking, agreement or instrument that would
constitute indebtedness), (b) is directly or indirectly liable (as a guarantor
or otherwise), or (c) constitutes the lender; and (ii) no default with respect
to which would permit (upon notice, lapse of time or both) any holder of any
other indebtedness of the Company or any of its Subsidiaries to declare a
default under such other indebtedness or cause the payment thereof to be
accelerated or payable prior to its stated maturity; and (iii) as to which the
lenders have been notified in writing that they will not have any recourse to
the stock or assets of the Company or any Subsidiary other than the assets that
were acquired with the proceeds of such transaction or the project financed
with the proceeds of such transaction (and the proceeds thereof).

                 "Non-Recourse Subsidiary" has the meaning specified in the
definition of Non-Recourse Obligation in this Section 1.01.

                 "Notice of Default" means a written notice of the kind
specified in Section 5.01(4) or 5.01(5).

                 "Officers' Certificate" means a certificate signed by any of
the Chairman of the Board, a Vice Chairman of the Board, the President or a
Vice President, and by any of the Treasurer, an Assistant Treasurer, the
Secretary or an Assistant Secretary, of the Company, and delivered to the
Trustee. One of the officers signing an Officers' Certificate given pursuant to
Section 10.04 shall be the principal executive, financial or accounting officer
of the Company.

                 "Opinion of Counsel" means a written opinion of counsel, who
may be counsel for the Company.

                 "Optional Redemption" has the meaning specified in Section
11.02.

                 "Other Event" has the meaning specified in Section 13.04.
<PAGE>   12
                                                                               6




                 "Outstanding", when used with respect to Securities, means, as
of the date of determination, all Securities theretofore authenticated and
delivered under this Indenture, except:

                 (i)  Securities theretofore cancelled by the Trustee or
delivered to the Trustee for cancellation;

                 (ii)  Securities for whose payment or redemption money in the
         necessary amount has been theretofore deposited with the Trustee or
         any Paying Agent (other than the Company) in trust or set aside and
         separated in trust by the Company (if the Company shall act as its own
         Paying Agent) for the Holders of such Securities; provided that, if
         such Securities are to be redeemed, notice of such redemption shall
         have been duly given pursuant to this Indenture or provision therefor
         satisfactory to the Trustee shall have been made;

                 (iii)  Securities which have been paid pursuant to Section
         3.07 or in exchange for or in lieu of which other Securities have been
         authenticated and delivered pursuant to this Indenture, other than any
         such Securities in respect of which there shall have been presented to
         the Trustee proof satisfactory to it that such Securities are held by
         a bona fide purchaser in whose hands such Securities are valid
         obligations of the Company; and

                 (iv) Securities which have been defeased pursuant to Section
         15.02;

provided, however, that in determining whether the Holders of the requisite
principal amount of the Outstanding Securities have given, made or taken any
request, demand, authorization, direction, notice, consent, waiver or other
action hereunder as of any date, Securities owned by the Company or any other
obligor upon the Securities or any Affiliate of the Company or of such other
obligor shall be disregarded and deemed not to be Outstanding, except that, in
determining whether the Trustee shall be protected in relying upon any such
request, demand, authorization, direction, notice, consent, waiver or other
action, only Securities which a Responsible Officer of the Trustee knows to be
so owned shall be so disregarded.  Securities so owned which have been pledged
in good faith may be regarded as Outstanding if the pledgee establishes to the
satisfaction of the Trustee the pledgee's right so to act with respect to such
Securities and that the pledgee is not the Company or any other obligor upon
the Securities or any Affiliate of the Company or of such other obligor.

                 "Paying Agent" means any Person authorized by the Company to
pay the principal of and premium, if any (including the Make-Whole Payment, if
any), or interest on any Securities on behalf of the Company.

                 "Person" means any individual, corporation, partnership, joint
venture, trust, unincorporated organization or government or any agency or
political subdivision thereof.

                 "Predecessor Security" of any particular Security means every
previous Security evidencing all or a portion of the same debt as that
evidenced by such particular Security; and, for the purposes of this
definition, any Security authenticated and delivered under Section 3.06 in
exchange for or in lieu of a mutilated, destroyed, lost or stolen
<PAGE>   13
                                                                               7




Security shall be deemed to evidence the same debt as the mutilated, destroyed,
lost or stolen Security.

                 "Provisional Redemption" has the meaning specified in Section
11.01.

                 "Provisional Redemption Date" has the meaning specified in
Section 11.01.

                 "Purchased Shares" has the meaning specified in Section 13.04.

                 "Qualified Institutional Buyer" means a "qualified
institutional buyer" as defined in Rule 144A.

                 "Redemption Date", when used with respect to any Security to
be redeemed, means the date fixed for such redemption by or pursuant to this
Indenture.

                 "Redemption Notice Date" has the meaning specified in Section
11.01.

                 "Redemption Price", when used with respect to any Security to
be redeemed, means the price at which it is to be redeemed as set forth in the
Securities.

                 "Reference Date" has the meaning specified in Section 13.04.

                 "Registration Default" has the meaning specified in Section
10.11.

                 "Registration Rights Agreement" has the meaning specified in
Section 10.11.

                 "Regular Record Date" for the interest payable on any Interest
Payment Date means the June 1 or December 1 (whether or not a Business Day), as
the case may be, next preceding such Interest Payment Date.

                 "Repurchase Date" has the meaning specified in Section 14.01.

                 "Repurchase Price" has the meaning specified in Section 14.01.

                 "Responsible Officer", when used with respect to the Trustee,
means any officer in the corporate trust department of the Trustee to whom any
matter has been referred because of such officer's knowledge and familiarity
with the particular subject.

                 "Restricted Global Security" has the meaning specified in
Section 2.01.

                 "Restricted Security" means a Security required to bear the
restricted securities legend set forth in Section 2.02.

                 "Rule 144A" means Rule 144A under the Securities Act (or any
successor provision), as it may be amended from time to time.

                 "Rule 144A Information" has the meaning specified in Section
10.09.
<PAGE>   14
                                                                               8




                 "Securities" has the meaning stated in the first recital of
this Indenture and more particularly means any Securities authenticated and
delivered under this Indenture and "Security" means one of such Securities.

                 "Securities Act" means the Securities Act of 1933 as it may be
amended from time to time, and any successor act thereto, and the rules and
regulations of the Commission promulgated thereunder.

                 "Security Register" has the meaning specified in Section 3.05.

                 "Security Registration" has the meaning specified in Section
3.05.

                 "Senior Indebtedness" means the principal of and premium, if
any, and interest on all indebtedness of the Company for money borrowed, other
than the Securities, whether outstanding on the date of execution of the
Indenture or thereafter created, incurred, guaranteed or assumed, except such
indebtedness that by the terms of the instrument or instruments by which such
indebtedness was created or incurred expressly provides that it (i) is junior
in right of payment to the Securities or any other indebtedness of the Company
for borrowed money or (ii) ranks pari passu in right of payment to the
Securities.  The term "indebtedness for money borrowed" when used with respect
to the Company is defined to mean (i) any obligation of, or any obligation
guaranteed by, the Company for the repayment of borrowed money, whether or not
evidenced by bonds, debentures, notes or other written instruments, (ii) all
obligations of the Company with respect to interest rate hedging agreements to
hedge interest rates relating to Senior Indebtedness of the Company, (iii) any
deferred payment obligation of, or any such obligation guaranteed by, the
Company for the payment of the purchase price of property or assets evidenced
by a note or similar instrument, and (iv) any obligation of, or any such
obligation guaranteed by, the Company for the payment of rent or other amounts
under a lease of property or assets which obligation is required to be
classified and accounted for as a capitalized lease on the balance sheet of the
Company under generally accepted accounting principles.

                 "Shelf Registration Statement" has the meaning specified in
Section 10.11.

                 "Special Record Date" for the payment of any Defaulted
Interest means a date fixed by the Trustee pursuant to Section 3.07.

                 "Stated Maturity", when used with respect to any Security or
any installment of principal thereof or interest thereon, means the date
specified in such Security as the fixed date on which the principal of such
Security or such installment of principal or interest is due and payable.

                 "Subsidiary" means a corporation more than 50% of the
outstanding voting stock of which is owned, directly or indirectly, by the
Company or by one or more other Subsidiaries, or by the Company and one or more
other Subsidiaries.  For the purposes of this definition, "voting stock" means
stock which ordinarily has voting power for the election of directors, whether
at all times or only so long as no senior class of stock has such voting power
by reason of any contingency.

                 "Surrendered Securities" has the meaning specified in Section
2.06.
<PAGE>   15
                                                                               9




                 "Trading Day" means each Monday, Tuesday, Wednesday, Thursday
and Friday, other than any day on which securities are not traded on the
applicable securities exchange or in the applicable securities market.

                 "Transfer Restricted Securities" has the meaning specified in
the Registration Rights Agreement.

                 "Trust Indenture Act" means the Trust Indenture Act of 1939 as
in force at the date as of which this instrument was executed and the rules and
regulations thereunder; provided, however, that in the event the Trust
Indenture Act of 1939 or such rules and regulations are amended after such
date, "Trust Indenture Act" means, to the extent required by any such
amendment, the Trust Indenture Act of 1939 and such rules and regulations as so
amended.

                 "Trustee" means the Person named as the "Trustee" in the first
paragraph of this instrument until a successor Trustee shall have become such
pursuant to the applicable provisions of this Indenture, and thereafter
"Trustee" shall mean such successor Trustee.

                 "United States" means the United States of America (including
the States thereof and the District of Columbia), its territories, its
possessions and other areas subject to its jurisdiction.

                 "U.S. Government Obligation" has the meaning specified in
Section 15.04.

                 "Vice President", when used with respect to the Company or the
Trustee, means any vice president, whether or not designated by a number or a
word or words added before or after the title "vice president".

                 SECTION 1.02.  Compliance Certificates and Opinions.  Upon any
application or request by the Company to the Trustee to take any action under
any provision of this Indenture, the Company shall furnish to the Trustee an
Officers' Certificate, if to be given by an officer of the Company, or an
Opinion of Counsel, if to be given by counsel, stating that all conditions
precedent, if any, provided for in this Indenture relating to the proposed
action have been complied with.

                 Every certificate or opinion with respect to compliance with a
condition or covenant provided for in this Indenture shall include:

                 (a)  a statement that each individual signing such certificate
         or opinion has read such covenant or condition and the definitions
         herein relating thereto;

                 (b)  a brief statement as to the nature and scope of the
         examination or investigation upon which the statements or opinions
         contained in such certificate or opinion are based;

                 (c)  a statement that, in the opinion of each such individual,
         he has made such examination or investigation as is necessary to
         enable him to express an informed opinion as to whether or not such
         covenant or condition has been complied with; and
<PAGE>   16
                                                                              10




                 (d)  a statement as to whether, in the opinion of each such
         individual, such condition or covenant has been complied with.

                 SECTION 1.03.  Form of Documents Delivered to Trustee.  In any
case where several matters are required to be certified by, or covered by an
opinion of, any specified Person, it is not necessary that all such matters be
certified by, or covered by the opinion of, only one such Person, or that they
be so certified or covered by only one document, but one such Person may
certify or give an opinion with respect to some matters and one or more other
such Persons as to other matters, and any such Person may certify or give an
opinion as to such matters in one or several documents.

                 Any certificate or opinion of an officer of the Company may be
based, insofar as it relates to legal matters, upon a certificate or opinion
of, or representations by, counsel, unless such officer knows, or in the
exercise of reasonable care should know, that the certificate or opinion or
representations with respect to the matters upon which his certificate or
opinion is based are erroneous. Any such certificate or Opinion of Counsel may
be based, insofar as it relates to factual matters, upon a certificate or
opinion of, or representations by, an officer or officers of the Company
stating that the information with respect to such factual matters is in the
possession of the Company, unless such counsel knows, or in the exercise of
reasonable care should know, that the certificate or opinion or representations
with respect to such matters are erroneous.

                 Where any Person is required to make, give or execute two or
more applications, requests, consents, certificates, statements, opinions or
other instruments under this Indenture, they may, but need not, be consolidated
and form one instrument.

                 SECTION 1.04.  Acts of Holders; Record Dates.  Any request,
demand, authorization, direction, notice, consent, waiver or other action
provided or permitted by this Indenture to be given or taken by Holders may be
embodied in and evidenced by one or more instruments of substantially similar
tenor signed by such Holders in person or by an agent duly appointed in
writing; and, except as herein otherwise expressly provided, such action shall
become effective when such instrument or instruments are delivered to the
Trustee and, where it is hereby expressly required, to the Company.  Such
instrument or instruments (and the action embodied therein and evidenced
thereby) are herein sometimes referred to as the "Act" of the Holders signing
such instrument or instruments. Proof of execution of any such instrument or of
a writing appointing any such agent shall be sufficient for any purpose of this
Indenture and (subject to Section 6.01) conclusive in favor of the Trustee and
the Company, if made in the manner provided in this Section 1.04.

                 The fact and date of the execution by any Person of any such
instrument or writing may be proved by the affidavit of a witness of such
execution or by a certificate of a notary public or other officer authorized by
law to take acknowledgments of deeds, certifying that the individual signing
such instrument or writing acknowledged to him the execution thereof.  Where
such execution is by a signer acting in a capacity other than his individual
capacity, such certificate or affidavit shall also constitute sufficient proof
of his authority.  The fact and date of the execution of any such instrument or
writing, or the authority of the Person executing the same, may also be proved
in any other manner which the Trustee deems sufficient.

                 The ownership of Securities shall be proved by the Security
Register.
<PAGE>   17
                                                                              11




                 Any request, demand, authorization, direction, notice,
consent, waiver or other Act of the Holder of any Security shall bind every
future Holder of the same Security and the Holder of every Security issued upon
the registration of transfer thereof or in exchange therefor or in lieu thereof
in respect of anything done, omitted or suffered to be done by the Trustee or
the Company in reliance thereon, whether or not notation of such action is made
upon such Security.

                 The Company may set any day as a record date for the purpose
of determining the Holders of Outstanding Securities entitled to give or take
any request, demand, authorization, direction, notice, consent, waiver or other
action provided or permitted by this Indenture to be given or taken by Holders
of Securities; provided that the Company may not set a record date for, and the
provisions of this paragraph shall not apply with respect to, the giving or
making of any notice, declaration, request or direction referred to in the next
paragraph. If any record date is set pursuant to this paragraph, the Holders of
Outstanding Securities on such record date, and no other Holders, shall be
entitled to take the relevant action, whether or not such Holders remain
Holders after such record date; provided that no such action shall be effective
hereunder unless taken on or prior to the applicable Expiration Date by Holders
of the requisite principal amount of Outstanding Securities on such record
date; and provided further, that for the purpose of determining whether Holders
of the requisite principal amount of such Securities have taken such action, no
Security shall be deemed to have been Outstanding on such record date unless it
is also Outstanding on the date such action is to become effective.  Nothing in
this paragraph shall prevent the Company from setting a new record date for any
action for which a record date has previously been set pursuant to this
paragraph (whereupon the record date previously set shall automatically and
with no action by any Person be cancelled and of no effect), nor shall anything
in this paragraph be construed to render ineffective any action taken by
Holders of the requisite principal amount of Outstanding Securities on the date
such action is taken.  Promptly after any record date is set pursuant to this
paragraph, the Company, at its own expense, shall cause notice of such record
date, the proposed action by Holders and the applicable Expiration Date to be
given to the Trustee in writing and to each Holder of Securities in the manner
set forth in Section 1.06.

                 The Trustee may set any day as a record date for the purpose
of determining the Holders of Outstanding Securities entitled to join in the
giving or making of (i) any Notice of Default, (ii) any declaration of
acceleration referred to in Section 5.02, (iii) any request to institute
proceedings referred to in Section 5.07(2), or (iv) any direction referred to
in Section 5.12. If any record date is set pursuant to this paragraph, the
Holders of Outstanding Securities on such record date, and no other Holders,
shall be entitled to join in such notice, declaration, request or direction,
whether or not such Holders remain Holders after such record date; provided
that no such action shall be effective hereunder unless taken on or prior to
the applicable Expiration Date by Holders of the requisite principal amount of
Outstanding Securities on such record date; and provided, further, that for the
purpose of determining whether Holders of the requisite principal amount of
such Securities have taken such action, no Security shall be deemed to have
been Outstanding on such record date unless it is also Outstanding on the date
such action is to become effective. Nothing in this paragraph shall be
construed to prevent the Trustee from setting a new record date for any action
(whereupon the record date previously set shall automatically and without any
action by any Person be cancelled and of no effect), nor shall anything in this
paragraph be construed to render ineffective any action taken by Holders of the
requisite principal amount of Outstanding Securities on the
<PAGE>   18
                                                                              12




date such action is taken.  Promptly after any record date is set pursuant to
this paragraph, the Trustee, at the Company's expense, shall cause notice of
such record date, the proposed action by Holders and the applicable Expiration
Date to be given to the Company in writing and to each Holder of Securities in
the manner set forth in Section 1.06.

                 With respect to any record date set pursuant to this Section,
the party hereto that sets such record date may designate any day as the
"Expiration Date" and from time to time may change the Expiration Date to any
earlier or later day; provided that no such change shall be effective unless
notice of the proposed new Expiration Date is given to the other party hereto
in writing, and to each Holder of Securities in the manner set forth in Section
1.06, on or before the existing Expiration Date.  Notwithstanding the
foregoing, no Expiration Date shall be later than the 180th day after the
applicable record date and, if an Expiration Date is not designated with
respect to any record date set pursuant to this Section, the party hereto that
set such record date shall be deemed to have designated the 180th day after
such record date as the Expiration Date with respect thereto.

                 Without limiting the foregoing, a Holder entitled hereunder to
take any action hereunder with regard to any particular Security may do so with
regard to all or any part of the principal amount of such Security or by one or
more duly appointed agents, each of which may do so pursuant to such
appointment with regard to all or any part of such principal amount.

                 SECTION 1.05.  Notices, etc. to Trustee and Company.  Any
request, demand, authorization, direction, notice, consent, waiver or Act of
Holders or other document provided or permitted by this Indenture to be made
upon, given or furnished to, or filed with,

                 (1) the Trustee by any Holder or by the Company shall be
sufficiently given if made, given, furnished or filed in writing to or with the
Trustee at its Corporate Trust Office, Attention: Corporate Trust
Administration, or at any other address previously furnished in writing to the
Company by the Trustee, or

                 (2) the Company by the Trustee or by any Holder shall be
sufficiently given (unless otherwise herein expressly provided) if in writing
and mailed, first-class postage prepaid, to the Company, addressed to it at the
address of its principal office specified in the first paragraph of this
instrument or at any other address previously furnished in writing to the
Trustee by the Company.

                 SECTION 1.06. Notice to Holders; Waiver.  Where this Indenture
provides for notice to Holders of any event, such notice shall be sufficiently
given (unless otherwise herein expressly provided) if in writing and mailed,
first-class postage prepaid, to each Holder affected by such event, at his
address as it appears in the Security Register, not later than the latest date
(if any), and not earlier than the earliest date (if any), prescribed for the
giving of such notice.  In any case where notice to Holders is given by mail,
neither the failure to mail such notice, nor any defect in any notice so
mailed, to any particular Holder shall affect the sufficiency of such notice
with respect to other Holders.  Where this Indenture provides for notice in any
manner, such notice may be waived in writing by the Person entitled to receive
such notice, either before or after the event, and such waiver shall be the
equivalent of such notice.  Waivers of notice by Holders shall be
<PAGE>   19
                                                                              13




filed with the Trustee, but such filing shall not be a condition precedent to
the validity of any action taken in reliance upon such waiver.

                 In case by reason of the suspension of regular mail service or
by reason of any other cause it shall be impracticable to give such notice by
mail, then such notification as shall be made with the approval of the Trustee
shall constitute a sufficient notification for every purpose hereunder.

                 SECTION 1.07. Conflict with Trust Indenture Act.  If any
provision hereof limits, qualifies or conflicts with a provision of the Trust
Indenture Act which is required under such Act to be a part of and govern this
Indenture, the latter provision shall control.  If any provision of this
Indenture modifies or excludes any provision of the Trust Indenture Act which
may be so modified or excluded, the latter provision shall be deemed to apply
to this Indenture as so modified or to be excluded, as the case may be. To the
extent a Security conflicts with a provision in the Indenture, the Indenture
governs.

                 SECTION 1.08.  Effect of Headings and Table of Contents.  The
Article and Section headings herein and the Table of Contents are for
convenience only and shall not affect the construction hereof.

                 SECTION 1.09.  Successors and Assigns.  All covenants and
agreements in this Indenture by the Company shall bind its successors and
assigns, whether so expressed or not.

                 SECTION 1.10.  Severability Clause.  In case any provision in
this Indenture or in the Securities shall be invalid, illegal or unenforceable,
the validity, legality and enforceability of the remaining provisions shall not
in any way be affected or impaired thereby.

                 SECTION 1.11.  Benefits of Indenture.  Nothing in this
Indenture or in the Securities, express or implied, shall give to any Person,
other than the parties hereto and their successors hereunder, the holders of
Senior Indebtedness and the Holders of Securities, any benefit or any legal or
equitable right, remedy or claim under this Indenture.

                 SECTION 1.12. Governing Law.  THIS INDENTURE AND THE
SECURITIES SHALL BE GOVERNED BY AND CONSTRUED IN ACCORDANCE WITH THE LAW OF THE
STATE OF NEW YORK WITHOUT REGARD TO CONFLICT OF LAWS PRINCIPLES.

                 SECTION 1.13.  Legal Holidays.  In any case where any Interest
Payment Date, Redemption Date, Repurchase Date or Stated Maturity of any
Security or the last date on which a Holder has the right to convert his
Securities shall not be a Business Day then (notwithstanding any other
provision of this Indenture or of the Securities) payment of interest or
principal and premium, if any (including the Make-Whole Payment, if any), or
conversion of the Securities need not be made on such date, but may be made on
the next succeeding Business Day with the same force and effect as if made on
the Interest Payment Date, Redemption Date, Repurchase Date or at the Stated
Maturity, or on such last day for conversion; provided that no interest shall
accrue for the period from and after such Interest Payment Date, Redemption
Date, Repurchase Date or Stated Maturity, as the case may be.
<PAGE>   20
                                                                              14



                                   ARTICLE II

                                 Security Forms

                 SECTION 2.01.  Forms Generally.  The Securities, the
conversion notice and the Trustee's certificates of authentication shall be in
substantially the forms set forth in this Article, with such appropriate
insertions, omissions, substitutions and other variations as are required or
permitted by this Indenture, and may have such letters, numbers or other marks
of identification and such legends or endorsements placed thereon as may be
required to comply with the rules of any securities exchange or Depositary
therefor or as may, consistently herewith, be determined by the officers
executing such Securities, as evidenced by their execution of the Securities.

                 The definitive Securities shall be printed, lithographed or
engraved on steel engraved borders or may be produced in any other manner, all
as determined by the officers executing such Securities, as evidenced by their
execution of such Securities.

                 In certain cases described elsewhere herein, the legends set
forth in the first four paragraphs of Section 2.02 may be omitted from
Securities issued hereunder.

                 Upon their original issuance, Securities offered and sold in
reliance on Rule 144A as provided in the Purchase Agreement, shall be issued in
the form of a single Global Security in definitive, fully registered form
without interest coupons, substantially in the form of Security set forth in
Sections 2.02 and 2.03, with such applicable legends as are provided for in
Section 2.02, except as otherwise permitted herein.  Such Global Security shall
be registered in the name of DTC, as Depositary, or its nominee, duly executed
by the Company and authenticated by the Trustee as hereinafter provided, and
deposited with the Trustee, as custodian for DTC, for credit by DTC to the
respective accounts of beneficial owners of the Securities represented thereby
(or such other accounts as they may direct).  Such Global Security, together
with its Successor Securities which are Global Securities, are collectively
herein called the "Restricted Global Security".

                 Except as provided in this Section 2.01 or Section 3.05,
owners of beneficial interests in Global Securities will not be entitled to
receive physical delivery of certificated Securities.  Upon transfer of
definitive Securities to a Qualified Institutional Buyer, such definitive
Securities will, unless the Restricted Global Security has previously been
exchanged, be exchanged for an interest in the Restricted Global Security
pursuant to the provisions of Section 3.05.

                 Neither the Company nor the Trustee shall have any
responsibility for any defect in the CUSIP number that appears on any Security,
check, advice of payment or redemption or repurchase notice, and any such
document may contain a statement to the effect that CUSIP numbers have been
assigned by an independent service for convenience of reference and that
neither the Company nor the Trustee shall be liable for any inaccuracy in such
numbers.
<PAGE>   21
                                                                              15




                 SECTION 2.02.  Form of Face of Security.

                 [INCLUDE IF SECURITY IS A RESTRICTED SECURITY OR A DEFINITIVE
SECURITY OTHER THAN A RESTRICTED GLOBAL SECURITY:

                 THIS SECURITY (OR ITS PREDECESSOR) WAS ORIGINALLY ISSUED IN A
TRANSACTION EXEMPT FROM REGISTRATION UNDER THE UNITED STATES SECURITIES ACT OF
1933 (THE "SECURITIES ACT"), AND THIS SECURITY AND THE COMMON STOCK ISSUABLE
UPON THE CONVERSION THEREOF MAY NOT BE OFFERED, SOLD OR OTHERWISE TRANSFERRED
IN THE ABSENCE OF SUCH REGISTRATION OR IN A TRANSACTION EXEMPT FROM, OR NOT
SUBJECT TO, THE SECURITIES ACT. EACH PURCHASER OF THIS SECURITY IS HEREBY
NOTIFIED THAT THE SELLER OF THIS SECURITY, AND THE COMMON STOCK ISSUABLE UPON
THE CONVERSION THEREOF, MAY BE RELYING ON THE EXEMPTION FROM THE PROVISIONS OF
SECTION 5 OF THE SECURITIES ACT PROVIDED BY RULE 144A THEREUNDER.

                 THE HOLDER OF THIS SECURITY AGREES FOR THE BENEFIT OF THE
COMPANY THAT (A) THIS SECURITY AND THE COMMON STOCK ISSUABLE UPON THE
CONVERSION THEREOF MAY BE OFFERED, RESOLD, PLEDGED OR OTHERWISE TRANSFERRED,
ONLY (I) TO A PERSON WHOM THE SELLER REASONABLY BELIEVES IS A QUALIFIED
INSTITUTIONAL BUYER (AS DEFINED IN RULE 144A UNDER THE SECURITIES ACT) IN A
TRANSACTION MEETING THE REQUIREMENTS OF RULE 144A, (II) PURSUANT TO AN
EXEMPTION FROM REGISTRATION UNDER THE SECURITIES ACT PROVIDED BY RULE 144
THEREUNDER (IF AVAILABLE) OR (III) PURSUANT TO AN EFFECTIVE REGISTRATION
STATEMENT UNDER THE SECURITIES ACT, IN EACH OF CASES (I) THROUGH (III) IN
ACCORDANCE WITH ANY APPLICABLE SECURITIES LAWS OF ANY STATE OF THE UNITED
STATES, AND (B) THE HOLDER WILL, AND EACH SUBSEQUENT HOLDER IS REQUIRED TO,
NOTIFY ANY PURCHASER OF THIS SECURITY AND ANY SHARES OF COMMON STOCK ISSUABLE
UPON THE CONVERSION THEREOF OF THE RESALE RESTRICTIONS REFERRED TO IN (A)
ABOVE.]

                 [INCLUDE IF SECURITY IS A RESTRICTED GLOBAL SECURITY:

                 THE SECURITIES EVIDENCED BY THIS GLOBAL SECURITY (OR ITS
PREDECESSOR) WERE ORIGINALLY ISSUED IN A TRANSACTION EXEMPT FROM REGISTRATION
UNDER THE UNITED STATES SECURITIES ACT OF 1933 (THE "SECURITIES ACT"), AND SUCH
SECURITIES AND THE COMMON STOCK ISSUABLE UPON THE CONVERSION THEREOF MAY NOT BE
OFFERED, SOLD OR OTHERWISE TRANSFERRED IN THE ABSENCE OF SUCH REGISTRATION OR
IN A TRANSACTION EXEMPT FROM, OR NOT SUBJECT TO, THE SECURITIES ACT.  EACH
PURCHASER OF ANY BENEFICIAL INTEREST IN THE SECURITIES IS HEREBY NOTIFIED THAT
THE SELLER OF SUCH BENEFICIAL INTEREST MAY BE RELYING ON THE EXEMPTION FROM THE
PROVISIONS OF SECTION 5 OF THE SECURITIES ACT PROVIDED BY RULE 144A THEREUNDER.
<PAGE>   22
                                                                              16




                 EACH BENEFICIAL OWNER OF AN INTEREST IN ANY OF THE SECURITIES
EVIDENCED BY THIS GLOBAL SECURITY (INCLUDING ANY PARTICIPANT IN THE DEPOSITARY
HOLDING THE GLOBAL SECURITY THAT IS SHOWN AS HOLDING SUCH AN INTEREST ON THE
RECORDS OF SUCH DEPOSITARY AND EACH BENEFICIAL OWNER THAT HOLDS THROUGH SUCH
PARTICIPANT) AGREES FOR THE BENEFIT OF THE COMPANY THAT (A) ANY BENEFICIAL
INTEREST IN THE SECURITIES AND THE COMMON STOCK ISSUABLE UPON THE CONVERSION
THEREOF MAY BE OFFERED, RESOLD, PLEDGED OR OTHERWISE TRANSFERRED, ONLY (I) TO A
PERSON WHOM THE SELLER REASONABLY BELIEVES IS A QUALIFIED INSTITUTIONAL BUYER
(AS DEFINED IN RULE 144A UNDER THE SECURITIES ACT) IN A TRANSACTION MEETING THE
REQUIREMENTS OF RULE 144A, (II) PURSUANT TO AN EXEMPTION FROM REGISTRATION
UNDER THE SECURITIES ACT PROVIDED BY RULE 144 THEREUNDER (IF AVAILABLE) OR
(III) PURSUANT TO AN EFFECTIVE REGISTRATION STATEMENT UNDER THE SECURITIES ACT,
IN EACH OF CASES (I) THROUGH (III) IN ACCORDANCE WITH ANY APPLICABLE SECURITIES
LAWS OF ANY STATE OF THE UNITED STATES, AND (B) THE BENEFICIAL OWNER WILL, AND
EACH SUBSEQUENT BENEFICIAL OWNER OF THIS SECURITY OR ANY SHARES OF COMMON STOCK
ISSUABLE UPON CONVERSION THEREOF IS REQUIRED TO, NOTIFY ANY PURCHASER OF ANY
BENEFICIAL INTEREST IN THE SECURITIES AND ANY SHARES OF COMMON STOCK ISSUABLE
UPON CONVERSION THEREOF FROM IT OF THE RESALE RESTRICTIONS REFERRED TO IN (A)
ABOVE.]

                 [INCLUDE IF SECURITY IS A GLOBAL SECURITY:

                 THIS SECURITY IS A GLOBAL SECURITY WITHIN THE MEANING OF THE
INDENTURE HEREINAFTER REFERRED TO AND IS REGISTERED IN THE NAME OF A DEPOSITARY
OR A NOMINEE THEREOF. THIS SECURITY MAY NOT BE EXCHANGED IN WHOLE OR IN PART
FOR A SECURITY REGISTERED, AND NO TRANSFER OF THIS SECURITY IN WHOLE OR IN PART
MAY BE REGISTERED, IN THE NAME OF ANY PERSON OTHER THAN SUCH DEPOSITARY OR A
NOMINEE THEREOF, EXCEPT IN THE LIMITED CIRCUMSTANCES DESCRIBED IN THE
INDENTURE.

                 UNLESS THIS CERTIFICATE IS PRESENTED BY AN AUTHORIZED
REPRESENTATIVE OF THE DEPOSITORY TRUST COMPANY, A NEW YORK CORPORATION ("DTC"),
NEW YORK, NEW YORK, TO THE COMPANY OR ITS AGENT FOR REGISTRATION OF TRANSFER,
EXCHANGE OR PAYMENT, AND ANY CERTIFICATE ISSUED IS REGISTERED IN THE NAME OF
CEDE & CO. OR IN SUCH OTHER NAME AS IS REQUESTED BY AN AUTHORIZED
REPRESENTATIVE OF DTC, AND ANY PAYMENT IS MADE TO CEDE & CO. OR TO SUCH OTHER
ENTITY AS IS REQUESTED BY AN AUTHORIZED REPRESENTATIVE OF DTC, ANY TRANSFER,
PLEDGE OR OTHER USE HEREOF FOR VALUE OR OTHERWISE BY OR TO ANY PERSON IS
WRONGFUL BECAUSE THE REGISTERED OWNER HEREOF, CEDE & CO., HAS AN INTEREST
HEREIN.]



                          Human Genome Sciences, Inc.
<PAGE>   23
                                                                              17




                   5% Convertible Subordinated Notes due 2006

No. ____                                               U.S. $_________________


[IF RESTRICTED GLOBAL SECURITY - CUSIP No. [                    ]]
[IF DEFINITIVE SECURITY - CUSIP No. [   ]]

                 Human Genome Sciences, Inc., a corporation duly organized and
existing under the laws of the State of Delaware (herein called the "Company",
which term includes any successor Person under the Indenture hereinafter
referred to), for value received, hereby promises to pay to ________, or
registered assigns, the principal sum of __________________________ United
States Dollars (U.S.$________ ) on December 15, 2006, and to pay interest
thereon from December 14, 1999, or from the most recent Interest Payment Date
to which interest has been paid or duly provided for, semi-annually on June 15
and December 15 in each year, commencing June 15, 2000, at the rate of 5% per
annum, until the principal hereof is paid or made available for payment.  The
interest so payable, and punctually paid or duly provided for, on any Interest
Payment Date will, as provided in such Indenture, be paid to the Person in
whose name this Security (or one or more Predecessor Securities) is registered
at the close of business on the Regular Record Date for such interest, which
shall be the June 1 or December 1 (whether or not a Business Day), as the case
may be, next preceding such Interest Payment Date.  Any such interest not so
punctually paid or duly provided for will forthwith cease to be payable to the
Holder on such Regular Record Date and may either be paid to the Person in
whose name this Security (or one or more Predecessor Securities) is registered
at the close of business on a Special Record Date for the payment of such
Defaulted Interest to be fixed by the Trustee, notice whereof shall be given to
Holders of Securities not less than 10 days prior to such Special Record Date,
or be paid at any time in any other lawful manner not inconsistent with the
requirements of any securities exchange on which the Securities may be listed,
and upon such notice as may be required by such exchange, all as more fully
provided in said Indenture.

                 Payment of the principal of, premium, if any (including the
Make-Whole Payment, if any), and interest (including payment of any Additional
Interest) on this Security will be made at the Corporate Trust Office, in such
coin or currency of the United States of America as at the time of payment is
legal tender for payment of public and private debts by a U.S. Dollar check
drawn on an account maintained with a bank in the Borough of Manhattan, The
City of New York; provided, however, that upon written application by the
Holder to the Security Registrar setting forth wire instructions not later than
15 days prior to the relevant payment date (in the case of payment of
principal) or not later than the relevant Record Date (in the case of payment
of interest), such Holder may receive payment by wire transfer of Dollars to a
U.S. Dollar account (such transfers to be made only to Holders of an aggregate
principal amount in excess of U.S.$2,000,000) maintained by the payee with a
bank in the United States or in Europe and designated by the payee to the
Security Registrar.

                 Reference is hereby made to the further provisions of this
Security set forth on the reverse hereof, which further provisions shall for
all purposes have the same effect as if set forth at this place.
<PAGE>   24
                                                                              18




                 Unless the certificate of authentication hereon has been
executed by the Trustee referred to on the reverse hereof by manual signature,
this Security shall not be entitled to any benefit under the Indenture or be
valid or obligatory for any purpose.

                 IN WITNESS WHEREOF, the Company has caused this instrument to
be duly executed.



                                     HUMAN GENOME SCIENCES, INC.


                                     By:
                                        -----------------------------------
                                        Name:
                                        Title:


                 SECTION 2.03.  Form of Reverse of Security.  This Security is
one of a duly authorized issue of Securities of the Company designated as its
5% Convertible Subordinated Notes due 2006 (herein called the "Securities"),
limited in aggregate principal amount to U.S.$150,000,000 (subject to increase
as provided in the Indenture herein defined up to an additional U.S.$50,000,000
aggregate principal amount), issued and to be issued under an Indenture, dated
as of December 14, 1999 (herein called the "Indenture"), between the Company
and The Bank of New York, as Trustee for the Holders of Securities issued under
said Indenture (herein called the "Trustee", which term includes any successor
trustee under the Indenture), to which Indenture and all indentures
supplemental thereto reference is hereby made for a statement of the respective
rights, limitations of rights, duties and immunities thereunder of the Company,
the Trustee, the holders of Senior Indebtedness and the Holders of the
Securities and of the terms upon which the Securities are, and are to be,
authenticated and delivered.

                 Subject to and upon compliance with the provisions of the
Indenture, the Holder of this Security is entitled, at his option, at any time
on or before the close of business on the Business Day immediately preceding
December 15, 2006, or in case this Security or a portion hereof is called for
redemption, then in respect of this Security or such portion hereof until and
including, but (unless the Company defaults in making the payment due upon
redemption or repurchase) not after, the close of business on the Business Day
immediately preceding the Redemption Date or Repurchase Date, as the case may
be, to convert this Security (or any portion of the principal amount hereof
which is U.S.$1,000 or an integral multiple thereof), at the principal amount
hereof, or of such portion, into fully paid and non-assessable shares of Common
Stock of the Company at a conversion price equal to U.S.$143.25 aggregate
principal amount of Securities for each share of Common Stock (or at the
current adjusted conversion price if an adjustment has been made as provided in
Article XIII of the Indenture) by surrender of this Security, duly endorsed or
assigned to the Company or in blank, to the Company at its office or agency in
the Borough of Manhattan, The City of New York, accompanied by the conversion
notice hereon executed by the Holder hereof evidencing such Holder's election
to convert this Security, or if less than the entire principal amount hereof is
to be converted, the portion hereof to be converted, and, in case such
surrender shall be made during the period from the close of business on any
Regular Record Date to the opening of business
<PAGE>   25
                                                                              19




on the corresponding Interest Payment Date (unless this Security or the portion
hereof being converted has been called for redemption on a Redemption Date
within such period between and including such Regular Record Date and such
Interest Payment Date), also accompanied by payment in funds acceptable to the
Company of an amount equal to the interest payable on such Interest Payment
Date on the principal amount of this Security then being converted. Subject to
the aforesaid requirement for payment of interest and, in the case of a
conversion after the close of business on any Regular Record Date and on or
before the corresponding Interest Payment Date, to the right of the Holder of
this Security (or any Predecessor Security) of record at such Regular Record
Date to receive an installment of interest (even if the Security has been
called for redemption on a Redemption Date within such period), no payment or
adjustment is to be made on conversion for interest accrued hereon or for
dividends on the Common Stock issued on conversion.  No fractions of shares or
scrip representing fractions of shares will be issued on conversion, but
instead of any fractional interest the Company shall pay a cash adjustment or
round up to the next higher whole share as provided in Article XIII of the
Indenture.  The conversion price is subject to adjustment as provided in
Article XIII of the Indenture.  In addition, the Indenture provides that in
case of certain reclassifications, consolidations, mergers, sales or transfers
of assets or other transactions pursuant to which the Common Stock is converted
into the right to receive other securities, cash or other property, the
Indenture shall be amended, without the consent of any Holders of Securities,
so that this Security, if then outstanding, will be convertible thereafter,
during the period this Security shall be convertible as specified above, only
into the kind and amount of securities, cash and other property receivable upon
the transaction by a holder of the number of shares of Common Stock into which
this Security might have been converted immediately prior to such transaction
(assuming such holder of Common Stock failed to exercise any rights of election
and received per share the kind and amount received per share by a plurality of
non-electing shares).

                 The Company will furnish to any Holder, upon request and
without charge, copies of the Certificate of Incorporation and By-laws of the
Company then in effect.  Any such request may be addressed to the Company.

                 The Securities may be provisionally redeemed by the Company,
in whole or in part, at any time prior to December 20, 2002, at a Redemption
Price equal to $1,000 per Security to be redeemed plus accrued and unpaid
interest, if any (including Additional Interest, if any) to the Redemption Date
if (i) the closing price of the Common Stock shall have exceeded 150% of the
conversion price then in effect for at least 20 Trading Days in any consecutive
30-Trading Day period ending on the Trading Day prior to the date of mailing of
the notice of Provisional Redemption, which date shall be no more than 60 nor
less than 20 days prior to the Redemption Date and (ii) the Shelf Registration
Statement is effective and available for use and is expected to remain
effective and available for use for the 30 days immediately following the
Redemption Date.  Upon any such Provisional Redemption, the Company shall make
an additional Make-Whole Payment in cash with respect to the Securities called
for redemption to Holders on the date of mailing of the notice of Provisional
Redemption in an amount equal to $150.00 per $1,000 Security, less the amount
of any interest actually paid on such Security prior to such date.  The Company
shall make the Make-Whole Payment on all Securities called for Provisional
Redemption, including any Securities converted after the date of mailing of the
notice of Provisional Redemption and prior to the Redemption Date.
<PAGE>   26
                                                                              20




                 The Securities are subject to redemption at the option of the
Company upon not less than 20 days' or more than 60 days' notice by mail, as a
whole or from time to time in part, at any time on or after December 20, 2002
through December 14, 2003 at 102.50% of the principal amount, and thereafter,
at the following Redemption Prices (expressed as percentages of the principal
amount), if redeemed during the 12-month period beginning on December 15 of the
years indicated,

<TABLE>
<CAPTION>
           Year                                       Redemption
           ----                                         Price
                                                      ----------
<S>                                                <C>
           2003 ...........................            101.67%

           2004 ...........................            100.83%

           2005 ...........................            100.00%
</TABLE>

and thereafter at a Redemption Price equal to 100% of the principal amount,
together in the case of any such redemption with accrued interest to (but not
including) the Redemption Date, but interest installments whose Stated Maturity
is on or prior to such Redemption Date will be payable to the Holders of such
Securities, or one or more Predecessor Securities, of record at the close of
business on the relevant Record Dates referred to on the face hereof, all as
provided in the Indenture.

                 In certain circumstances involving a Change in Control, each
Holder shall have the right to require the Company to redeem all or part of its
Securities at a repurchase price equal to 100% of the principal amount thereof,
together with accrued and unpaid interest through the Repurchase Date.

                 The Securities do not have the benefit of any sinking fund.

                 In the event of redemption, conversion or repurchase of this
Security in part only, a new Security or Securities for the unredeemed,
unconverted or unrepurchased portion hereof will be issued in the name of the
Holder hereof upon the cancellation hereof.

                 Subject to certain limitations in the Indenture, at any time
when the Company is not subject to Section 13 or 15(d) of the United States
Securities Exchange Act of 1934, as amended, upon the request of a Holder or
the holder of shares of Common Stock issued upon conversion thereof, the
Company will promptly furnish or cause to be furnished Rule 144A Information
(as defined below) to such Holder or such holder of shares of Common Stock
issued upon conversion, or to a prospective purchaser of any such security
designated by any such Holder or holder of shares of Common Stock, as the case
may be, to the extent required to permit compliance by such Holder or holder of
shares of Common Stock with Rule 144A under the United States Securities Act of
1933 (the "Securities Act"), in connection with the resale of any such
security.  "Rule 144A Information" shall be such information as is specified
pursuant to Rule 144A(d)(4) under the Securities Act (or any successor
provision thereto).

                 If this Security is a Transfer Restricted Security, then the
Holder of this Security [IF THIS SECURITY IS A GLOBAL SECURITY, THEN INSERT-
(including any Person that has a beneficial interest in this Security)] and the
Common Stock issuable upon conversion thereof is entitled to the benefits of a
Registration Rights Agreement,
<PAGE>   27
                                                                              21




dated as of December 14, 1999 (the "Registration Rights Agreement") executed by
the Company.  If a Registration Default occurs (as defined in the Registration
Rights Agreement and in the Indenture), Additional Interest will accrue on this
Security from and including the day following such Registration Default to but
excluding the day on which such Registration Default has been cured.
Additional Interest will be paid semi-annually in arrears, with the first
semi-annual payment due on the first Interest Payment Date in respect of the
Securities following the date on which such Additional Interest begins to
accrue, and will accrue at a rate per annum equal to an additional one-half of
one percent (0.50%) of the principal amount of the Securities.

                 Whenever in this Security there is a reference, in any
context, to the payment of the principal of, premium, if any (including the
Make-Whole Payment, if any), or interest on, or in respect of, any Security,
such mention shall be deemed to include mention of the payment of Additional
Interest payable as described in the preceding paragraph to the extent that, in
such context, Additional Interest is, was or would be payable in respect of
such Security and express mention of the payment of Additional Interest (if
applicable) in any provisions of this Security shall not be construed as
excluding Additional Interest in those provisions of this Security where such
express mention is not made.

                 The indebtedness evidenced by this Security is, to the extent
provided in the Indenture, subordinate and subject in right of payment to the
prior payment in full of all Senior Indebtedness, and this Security is issued
subject to the provisions of the Indenture with respect thereto.  Each Holder
of this Security, by accepting the same, (a) agrees to and shall be bound by
such provisions, (b) authorizes and directs the Trustee on his behalf to take
such action as may be necessary or appropriate to effectuate the subordination
so provided and (c) appoints the Trustee his attorney-in-fact for any and all
such purposes.

                 If an Event of Default shall occur and be continuing, the
principal of all the Securities may be declared due and payable in the manner
and with the effect provided in Article V of the Indenture.

                 The Indenture permits, with certain exceptions as therein
provided, the amendment thereof and the modification of the rights and
obligations of the Company and the rights of the Holders of the Securities
under the Indenture at any time by the Company and the Trustee with the consent
of the Holders of a majority in aggregate principal amount of the Securities at
the time Outstanding.  The Indenture also contains provisions permitting the
Holders of a majority in aggregate principal amount of the Securities at the
time Outstanding, on behalf of the Holders of all the Securities, to waive
compliance by the Company with certain provisions of the Indenture and certain
past defaults under the Indenture and their consequences.   Any such consent or
waiver by the Holder of this Security shall be conclusive and binding upon such
Holder and upon all future Holders of this Security and of any Security issued
upon the registration of transfer hereof or in exchange herefor or in lieu
hereof, whether or not notation of such consent or waiver is made upon this
Security.

                 No reference herein to the Indenture and no provision of this
Security or of the Indenture shall alter or impair the obligation of the
Company, which is absolute and unconditional, to pay the principal of, premium,
if any (including the Make-Whole Payment, if any), and interest on (including
Additional Interest) this Security at the times,
<PAGE>   28
                                                                              22




place and rate, and in the coin or currency,  herein prescribed or to convert
this Security as provided in the Indenture.

                 As provided in the Indenture and subject to certain
limitations therein set forth, the transfer of this Security is registrable in
the Security Register, upon surrender of this Security for registration of
transfer at the Corporate Trust Office duly endorsed by, or accompanied by a
written instrument of transfer in form satisfactory to the Company and the
Security Registrar duly executed by, the Holder hereof or his attorney duly
authorized in writing, and thereupon one or more new Securities, of authorized
denominations and for the same aggregate principal amount, will be issued to
the designated transferee or transferees.

                 The Securities are issuable only in registered form without
coupons in denominations of U.S.$1,000 and any integral multiple thereof.  As
provided in the Indenture and subject to certain limitations therein set forth,
Securities are exchangeable for a like aggregate principal amount of Securities
of a different authorized denomination, as requested by the Holder surrendering
the same.

                 No service charge shall be made for any such registration of
transfer or exchange, but the Company may require payment of a sum sufficient
to cover any tax or other governmental charge payable in connection therewith.

                 Prior to due presentment of this Security for registration of
transfer, the Company, the Trustee and any agent of the Company or the Trustee
may treat the Person in whose name this Security is registered as the owner
hereof for all purposes, whether or not payment of or on this Security is
overdue, and neither the Company, the Trustee nor any such agent shall be
affected by notice to the contrary.

                 Interest on this Security shall be computed on the basis of a
360-day year of twelve 30-day months.

                 All terms used in this Security which are defined in the
Indenture shall have the meanings assigned to them in the Indenture.

                 THE INDENTURE AND THIS SECURITY SHALL BE GOVERNED BY AND
CONSTRUED IN ACCORDANCE WITH THE LAWS OF THE STATE OF NEW YORK WITHOUT REGARD
TO CONFLICT OF LAWS PRINCIPLES.

                 SECTION 2.04.  Form of Trustee's Certificate of Authentication.

                 This is one of the Securities referred to in the
within-mentioned Indenture.

Dated:                            The Bank of New York, as Trustee

                              By
                                -----------------------------------------------
                                                           Authorized Signatory
<PAGE>   29
                                                                              23



                 SECTION 2.05.  Form of Conversion Notice.

                               CONVERSION NOTICE

To:  Human Genome Sciences, Inc.

                 The undersigned Holder of this Security hereby irrevocably
exercises the option to convert this Security, or the portion hereof (which is
U.S.$1,000 or an integral multiple thereof) below designated, at any time
following the date of original issuance thereof, into shares of Common Stock in
accordance with the terms of the Indenture referred to in this Security, and
directs that the shares issuable and deliverable upon conversion, together with
any check in payment for a fractional share and any Security representing any
unconverted principal amount hereof, be issued and delivered to the registered
owner hereof unless a different name has been provided below.  If shares or any
portion of this Security not converted are to be issued in the name of a person
other than the undersigned, the undersigned will pay all transfer taxes payable
with respect thereto and is delivering herewith a certificate in proper form
certifying that the applicable restrictions on transfer have been complied
with.  Any amount required to be paid by the undersigned on account of interest
accompanies this Security.

                 The Applicant hereby agrees that, promptly after request of
the Company, he or it will furnish such proof in support of this certification
as the Company or the Security Registrar for the Common Stock may, from time to
time, request.

Dated:
                                                   ----------------------------
                                                          Signature*



                                                   ----------------------------
                                                          Signature Guaranty

If shares or Securities are to be        Principal amount to be converted
registered in the name of a Person       (if less than all):
other than the Holder, please print      $_______ ,000
such Person's name and address:*



- ------------------------------------     --------------------------------------
              Name                                Social Security or
                                             Taxpayer Identification Number

- ------------------------------------
         Street Address

- ------------------------------------
     City, State and Zip Code

* Signature(s) must be guaranteed by an eligible guarantor institution (banks,
stock brokers, savings and loan associations and credit unions with membership
in an approved
<PAGE>   30
                                                                              24


signature guarantee medallion program) pursuant to Securities and Exchange
Commission Rule 17Ad-15 if shares of Common Stock are to be delivered, or
unconverted Securities are to be issued, other than to and in the name of the
registered owner.

                 SECTION 2.06.  Form of Certification.  Whenever any
certification is required to be given to evidence compliance with certain
restrictions relating to transfers of Restricted Securities contemplated by
Section 3.05(b)(iv), Section 3.05(c) or Section 13.02, such certification shall
be provided substantially in the form of the following certificate, with only
such changes as shall be approved by the Company and the Initial Purchaser.

                              TRANSFER CERTIFICATE

                 The undersigned Holder hereby certifies with respect to
U.S.$_________  principal amount of the above-captioned securities presented or
surrendered on the date hereof (the "Surrendered Securities") for registration
of transfer, or for exchange or conversion where the securities issuable upon
such exchange or conversion are to be registered in a name other than that of
the undersigned Holder (each such transaction being a "transfer"), that such
transfer complies with the restrictive legend set forth on the face of the
Surrendered Securities for the reason checked below:

- --------------            The transfer of the Surrendered Securities complies
                          with Rule 144 under the U.S. Securities Act of 1933
                          (the "Securities Act"); or

- --------------            The transfer of the Surrendered Securities complies
                          with Rule 144A under the Securities Act; or

- --------------            The transfer of the Surrendered Securities is
                          pursuant to an effective registration statement under
                          the Securities Act, the prospectus delivery
                          requirements under the Securities Act have been
                          satisfied with respect to such transfer, the
                          undersigned Holder is named as a "Selling
                          Securityholder" in the prospectus relating to such
                          registration statement, or in amendments or
                          supplements thereto, and the aggregate principal
                          amount of Surrendered Securities transferred are all
                          or a portion of the securities listed in such
                          prospectus opposite the undersigned's name.

Dated:____________________________*
*    To be dated the date of surrender.


                                  ---------------------------------------------
                                                  Signature

                                  (If the registered owner is a corporation,
                                  partnership or fiduciary, the title of the
                                  Person signing on behalf of such registered
                                  owner must be stated.)
<PAGE>   31
                                                                              25





                                  ARTICLE III

                                 The Securities

                 SECTION 3.01.  Title and Terms.  The aggregate principal
amount of Securities which may be authenticated and delivered under this
Indenture is limited to (a) U.S.$150,000,000 plus (b) such aggregate principal
amount (which may not exceed U.S.$50,000,000 principal amount) of Securities as
may be purchased by the Initial Purchaser pursuant to the Initial Purchaser's
option pursuant to the Purchase Agreement dated December 8, 1999, between the
Company and the Initial Purchaser, except for Securities authenticated and
delivered upon registration of transfer of, or in exchange for, or in lieu of,
other Securities pursuant to Sections 3.04, 3.05, 3.06, 9.06, 11.09, 13.02 or
14.05 and except for Securities which, pursuant to Section 3.03, are deemed
never to have been authenticated and delivered hereunder.

                 The Stated Maturity of the Securities shall be December 15,
2006, and they shall bear interest at the rate of 5% per annum, payable
semi-annually on December 15 and June 15, commencing January 1, 2000, until the
principal thereof is paid or made available for payment.

                 Payment of the principal of, premium, if any (including the
Make-Whole Payment, if any), and interest (including payment of any Additional
Interest) on this Security will be made at the Corporate Trust Office, in such
coin or currency of the United States of America as at the time of payment is
legal tender for payment of public and private debts by a U.S. Dollar check
drawn on an account maintained with a bank in the Borough of Manhattan, The
City of New York; provided, however, that upon written application by the
Holder to the Security Registrar setting forth wire instructions not later than
15 days prior to the relevant payment date (in the case of payment of
principal) or not later than the relevant Record Date (in the case of payment
of interest), such Holder may receive payment by wire transfer of Dollars to a
U.S. Dollar account (such transfers to be made only to Holders of an aggregate
principal amount in excess of U.S.$2,000,000) maintained by the payee with a
bank in the United States or in Europe and designated by the payee to the
Security Registrar.

                 The Securities shall be redeemable by the Company as provided
in Article XI.

                 The Securities shall be subordinated in right of payment to
the prior payment in full of Senior Indebtedness as provided in Article XII.

                 The Securities shall be convertible as provided in Article
XIII.

                 The Securities shall be subject to purchase by the Company at
the option of the Holder as provided in Article XIV.

                 SECTION 3.02.  Denominations.  The Securities shall be
issuable only in registered form without coupons and only in denominations of
U.S.$1,000 and any integral multiple thereof.

                 SECTION 3.03.  Execution, Authentication, Delivery and Dating.
The Securities shall be executed on behalf of the Company by any of its
Chairman of the
<PAGE>   32
                                                                              26



Board, its Vice Chairman of the Board, its President or one of its Vice
Presidents. The signature of any of these officers on the Securities may be
manual or facsimile.

                 Securities bearing the manual or facsimile signatures of
individuals who were at any time the proper officers of the Company shall bind
the Company, notwithstanding that such individuals or any of them have ceased
to hold such offices prior to the authentication and delivery of such
Securities or did not hold such offices at the date of such Securities.

                 At any time and from time to time after the execution and
delivery of this Indenture, the Company may deliver Securities of any series
executed by the Company to the Trustee for authentication, together with a
Company Order for the authentication and delivery of such Securities; and the
Trustee in accordance with such Company Order shall authenticate and deliver
such Securities as in this Indenture provided and not otherwise.

                 Each Security shall be dated the date of its authentication.

                 No Security shall be entitled to any benefit under this
Indenture or be valid or obligatory for any purpose unless there appears on
such Security a certificate of authentication substantially in the form
provided for herein executed by the Trustee by manual signature, and such
certificate upon any Security shall be conclusive evidence, and the only
evidence, that such Security has been duly authenticated and delivered
hereunder.

                 SECTION 3.04.  Global and Non-Global Securities.  (a)   Global
Securities.  (i)  Each Global Security authenticated under this Indenture shall
be registered in the name of the Depositary designated by the Company for such
Global Security or a nominee thereof and delivered to such Depositary or a
nominee thereof or custodian therefor, and each such Global Security shall
constitute a single Security for all purposes of this Indenture.

                 (ii)  Notwithstanding any other provision in this Indenture,
no Global Security may be exchanged in whole or in part for Securities
registered, and no transfer of a Global Security in whole or in part may be
registered, in the name of any Person other than the Depositary for such Global
Security or a nominee thereof unless (A) such Depositary (1) has notified the
Company that it is unwilling or unable to continue as Depositary for such
Global Security or (2) has ceased to be a clearing agency registered as such
under the Exchange Act or announces an intention permanently to cease business
or does in fact do so, (B) there shall have occurred and be continuing an Event
of Default with respect to such Global Security, or (C) the Company in its
discretion at any time determines not to have all the Securities represented by
a Global Security.  Any Global Security exchanged pursuant to clause (i) above
shall be so exchanged in whole and not in part and any Global Security
exchanged pursuant to clause (ii) or (iii) above may be exchanged in whole or
from time to time in part as directed by the Depositary.  Any Security issued
in exchange for a Global Security or any portion thereof shall be a Global
Security; provided that any such Security so issued that is registered in the
name of a Person other than the Depositary or a nominee thereof shall not be a
Global Security.

                 (iii)  If any Global Security is to be exchanged for other
Securities or cancelled in whole, it shall be surrendered by or on behalf of
the Depositary or its nominee to the Trustee, as Security Registrar, for
exchange or cancellation as provided in
<PAGE>   33
                                                                              27




this Article III.  If any Global Security is to be exchanged for other
Securities or cancelled in part, or if another Security is to be exchanged in
whole or in part for a beneficial interest in any Global Security, in each
case, as provided in Section 3.05, then either (i) such Global Security shall
be so surrendered for exchange or cancellation as provided in this Article III
or (ii) the principal amount thereof shall be reduced or increased by an amount
equal to the portion thereof to be so exchanged or cancelled, or equal to the
principal amount of such other Security to be so exchanged for a beneficial
interest therein, as the case may be, by means of an appropriate adjustment
made on the records of the Trustee, as Security Registrar, whereupon the
Trustee, in accordance with the Applicable Procedures, shall instruct the
Depositary or its authorized representative to make a corresponding adjustment
to its records.  Upon any such surrender or adjustment of a Global Security,
the Trustee shall, subject to Section 3.05(c) and as otherwise provided in this
Article III, authenticate and deliver any Securities issuable in exchange for
such Global Security (or any portion thereof) to or upon the order of, and
registered in such names as may be directed by, the Depositary or its
authorized representative.  Upon the request of the Trustee in connection with
the occurrence of any of the events specified in the preceding paragraph, the
Company shall promptly make available to the Trustee a reasonable supply of
Securities that are not in the form of Global Securities.  The Trustee shall be
entitled to rely upon any order, direction or request of the Depositary or its
authorized representative which is given or made pursuant to this Article III
if such order, direction or request is given or made in accordance with the
Applicable Procedures.

                 (iv)  Every Security authenticated and delivered upon
registration of transfer of, or in exchange for or in lieu of, a Global
Security or any portion thereof, whether pursuant to this Article III or
otherwise, shall be authenticated and delivered in the form of, and shall be, a
Global Security, unless such Security is registered in the name of a Person
other than the Depositary for such Global Security or a nominee thereof, in
which case such Security shall be authenticated and delivered in definitive,
fully registered form, without interest coupons.

                 (v)  The Depositary or its nominee, as registered owner of a
Global Security, shall be the Holder of such Global Security for all purposes
under the Indenture and the Securities, and owners of beneficial interests in a
Global Security shall hold such interests pursuant to the Applicable
Procedures.  Accordingly, any such owner's beneficial interest in a Global
Security will be shown only on, and the transfer of such interest shall be
effected only through, records maintained by the Depositary or its nominee or
its Agent Members and such owners of beneficial interests in a Global Security
will not be considered the owners or holders thereof.  Notwithstanding the
foregoing, nothing herein shall prevent the Company, the Trustee or any agent
of the Company or the Trustee from giving effect to any written certification,
proxy or other authorization furnished by the Depositary or such nominee, as
the case may be, or impair, as between the Depositary, its Agent Members and
any other person on whose behalf an Agent Member may act, the operation of
customary practices of such Persons governing the exercise of the rights of a
holder of any Security.

                 SECTION 3.05.  Registration; Registration of Transfer and
Exchange.  (a)  The Company shall cause to be kept at the Corporate Trust
Office of the Trustee a register (the register maintained in such office and in
any other office or agency designated pursuant to Section 10.02 being herein
sometimes collectively referred to as the "Security Register") in which,
subject to such reasonable regulations as it may prescribe, the Company shall
provide for the registration of Securities and of transfers and
<PAGE>   34
                                                                              28


exchanges thereof. The Trustee is hereby appointed "Security Registrar" for the
purpose of registering Securities and transfers and exchanges thereof as herein
provided. Upon surrender for registration of transfer or exchange of any
Security at an office or agency of the Company designated pursuant to Section
10.02 for such purpose, accompanied by a written instrument of transfer or
exchange in the form provided by the Company, the Company shall execute, and the
Trustee shall authenticate and deliver, in the name of the designated transferee
or transferees, one or more new Securities of any authorized denominations and
of a like aggregate principal amount.

                 (b)  Notwithstanding any other provisions of this Indenture or
the Securities, transfers and exchanges of Securities and beneficial interests
in a Global Security of the kinds specified in this Section 3.05(b) shall be
made only in accordance with this Section 3.05(b).

                 (i) Transfer of Global Security.  Other than as set forth in
     Section 3.04(a), a Global Security may not be transferred, in whole or in
     part, to any Person other than the Depositary or a nominee thereof, and no
     such transfer to any such other Person may be registered; provided that
     this Section 3.05(b)(i) shall not prohibit any transfer of a Security that
     is issued in exchange for a Global Security but is not itself a Global
     Security.  No transfer of a Security to any Person shall be effective
     under this Indenture or the Securities unless and until such Security has
     been registered in the name of such Person.  Nothing in this Section
     3.05(b)(i) shall prohibit or render ineffective any transfer of a
     beneficial interest in a Global Security effected in accordance with the
     other provisions of this Section 3.05(b).

                 (ii) Transfer of Beneficial Interests in the Global Security.
     Transfer of beneficial interests in the Global Security shall be effected
     through the Depositary, in accordance with this Indenture (including
     applicable restrictions on transfer set forth herein, if any) and the
     procedures of the Depositary therefor, if applicable.

                 (iii) Other Exchanges.  In the event that a Global Security or
     any portion thereof is exchanged for Securities other than Global
     Securities, such other Securities may in turn be exchanged (on transfer or
     otherwise) for Securities that are not Global Securities or for beneficial
     interests in a Global Security (if any is then outstanding) only in
     accordance with such procedures, which shall be substantially consistent
     with the provisions of this Section 3.05(b) (including the certification
     requirements set forth on the reverse of the Security intended to insure
     that transfers of beneficial interests in a Global Security comply with
     Rule 144A or Rule 144 under the Securities Act, as the case may be) and
     any Applicable Procedures, as may be from time to time adopted by the
     Company and the Trustee.

                 (iv) Transfer and Exchange of Definitive Securities.  When
     definitive Securities are presented to the Security Registrar with a
     request:

                          (A) to register the transfer of such definitive
                 Securities; or

                          (B) to exchange such definitive Securities for an
                 equal principal amount of definitive Securities of other
                 authorized denominations, the Security Registrar shall
                 register the transfer or make the exchange as requested if its
                 reasonable requirements for such transaction are met;
<PAGE>   35
                                                                              29




provided, however, that the definitive Securities surrendered for transfer or
exchange:

                                  (x) shall be duly endorsed or accompanied by
                          a written instrument of transfer in form reasonably
                          satisfactory to the Company and the Security
                          Registrar, duly executed by the Holder thereof or his
                          attorney duly authorized in writing; and

                                  (y) are being transferred or exchanged
                          pursuant to an effective registration statement under
                          the Securities Act, pursuant to Section 3.05(b)(v),
                          or pursuant to clause (1), (2) or (3) below, and are
                          accompanied by the following additional information
                          and documents, as applicable:

                                        (1) if such definitive Securities are
                                  being delivered to the Security Registrar by
                                  a Holder for registration in the name of such
                                  Holder, without transfer, a certification
                                  from such Holder to that effect (in the form
                                  set forth in Section 2.06); or

                                        (2) if such definitive Securities are
                                  being transferred to the Company, a
                                  certification to that effect (in the form set
                                  forth in Section 2.06); or

                                        (3) if such definitive Securities are
                                  being transferred pursuant to an exemption
                                  from registration in accordance with Rule
                                  144, (i) a certification to that effect (in
                                  the form set forth in Section 2.06) and (ii)
                                  if the Company or Security Registrar so
                                  requests, an opinion of counsel or other
                                  evidence reasonably satisfactory to them as
                                  to the compliance with the restrictions set
                                  forth in the legend set forth in Section
                                  2.02.

                 (v) Restrictions on Transfer of a Definitive Security for a
     Beneficial Interest in a Global Security.  A definitive Security may not
     be exchanged for a beneficial interest in a Global Security except upon
     satisfaction of the requirements set forth below.  Upon receipt by the
     Trustee of a definitive Security, duly endorsed or accompanied by
     appropriate instruments of transfer, in form satisfactory to the Trustee,
     together with:

                          (A) certification in the form set forth on the
                 reverse of the Security that such definitive Security is being
                 transferred to a Qualified Institutional Buyer in accordance
                 with Rule 144A; and

                          (B) written instructions directing the Trustee to
                 make, or to direct the Securities Registrar to make, an
                 adjustment on its books and records with respect to such
                 Global Security to reflect an increase in the aggregate
                 principal amount of the Securities represented by the Global
                 Security, such instructions to contain information regarding
                 the Depositary account to be credited with such increase,
<PAGE>   36
                                                                              30




     then the Trustee shall cancel such definitive Security and cause, or
     direct the Securities Registrar to cause, in accordance with the standing
     instructions and procedures existing between the Depositary and the
     Securities Registrar, the aggregate principal amount of Securities
     represented by the Global Security to be increased by the aggregate
     principal amount of the definitive Security to be exchanged and shall
     credit or cause to be credited to the account of the Person specified in
     such instructions a beneficial interest in the Global Security equal to
     the principal amount of the definitive Security so cancelled.  If no
     Global Securities are then outstanding, the Company shall issue and the
     Trustee shall authenticate, upon written order of the Company in the form
     of an Officers' Certificate, a new Global Security in the appropriate
     principal amount.

                 (c)  Subject to the succeeding paragraph, every Security shall
be subject to the restrictions on transfer provided in the legends required by
Section 2.02 to be applied to such Security.  Whenever any Security is
presented or surrendered for registration of transfer or for exchange for a
Security registered in a name other than that of the Holder, such Security must
be accompanied by a certificate in substantially the form set forth in Section
2.06, dated the date of such surrender and signed by the Holder of such
Security, as to compliance with such restrictions on transfer.  The Security
Registrar shall not be required to accept for such registration of transfer or
exchange any Security not so accompanied by a properly completed certificate.

                 (d)  The restrictions imposed by the legend set forth in the
first or second bracketed legend, as the case may be, of Section 2.02 upon the
transferability of any Security shall cease and terminate when such Security
has been sold pursuant to an effective registration statement under the
Securities Act, transferred in compliance with Rule 144 under the Securities
Act (or any successor provision thereto), or after the second anniversary of
the original issuance date of the Security (or such earlier date after which
the Security may be freely transferred without registration under the
Securities Act or without being subject to transfer restrictions pursuant to
the Securities Act, as may be provided in Rule 144(k) under the Securities Act
(or any successor provision thereto) or otherwise).  Any Security as to which
such restrictions on transfer shall have expired in accordance with their terms
or shall have terminated may, upon surrender of such Security for exchange to
the Security Registrar in accordance with the provisions of this Section 3.05
(accompanied, in the event that such restrictions on transfer have terminated
by reason of a transfer in compliance with Rule 144 or any successor provision,
by an opinion of counsel having substantial experience in practice under the
Securities Act and otherwise reasonably acceptable to the Company, addressed to
the Company and in form acceptable to the Company, to the effect that the
transfer of such Security has been made in compliance with Rule 144 or such
successor provision), be exchanged for a new Security, of like tenor and
aggregate principal amount, which shall not bear the restrictive legend set
forth in the first paragraph of Section 2.02.  The Company shall inform the
Trustee of the effective date of any registration statement registering the
Securities under the Securities Act.  The Trustee shall not be liable for any
action taken or omitted to be taken by it in good faith in accordance with the
aforementioned opinion of counsel or notice of an effective registration
statement.

                 (e)  As used in the preceding two paragraphs (c) and (d) of
this Section 3.05, the term "transfer" encompasses any sale, pledge, transfer,
hypothecation or other disposition of any Security.
<PAGE>   37
                                                                              31




                 (f)  No service charge shall be made for any registration of
transfer or exchange of Securities, but the Company may require payment of a
sum sufficient to cover any tax or other governmental charge that may be
imposed in connection with any registration of transfer or exchange of
Securities, other than exchanges pursuant to Section 3.04, 9.06, 11.09, 13.02
or 14.05 not involving any transfer.

                 (g)  The Company shall not be required (i) to issue, register
the transfer of or exchange any Security during a period beginning at the
opening of business 15 days before the day of the mailing of a notice of
redemption of Securities selected for redemption under Section 11.05 and ending
at the close of business on the day of such mailing, or (ii) to register the
transfer of or exchange any Security so selected for redemption in whole or in
part, except the unredeemed portion of any Security being redeemed in part.

                 SECTION 3.06.  Mutilated, Destroyed, Lost and Stolen
Securities.  If any mutilated Security is surrendered to the Trustee, the
Company shall execute and the Trustee shall authenticate and deliver in
exchange therefor a new Security of like tenor and principal amount and bearing
a number not contemporaneously outstanding.

                 If there shall be delivered to the Company and the Trustee (i)
evidence to their satisfaction of the destruction, loss or theft of any
Security and (ii) such security or indemnity as may be required by them to save
each of them and any agent of either of them harmless, then, in the absence of
notice to the Company or the Trustee that such Security has been acquired by a
bona fide purchaser, the Company shall execute and the Trustee shall
authenticate and deliver, in lieu of any such destroyed, lost or stolen
Security, a new Security of like tenor and principal amount and bearing a
number not contemporaneously outstanding.

                 In case any such mutilated, destroyed, lost or stolen Security
has become or is about to become due and payable, the Company in its
discretion, but subject to any conversion rights, may, instead of issuing a new
Security, pay such Security.

                 Upon the issuance, authentication and delivery by the Trustee
of any new Security under this Section 3.06, the Company may require the
payment of a sum sufficient to cover any tax or other governmental charge that
may be imposed in relation thereto and any other expenses (including the fees
and expenses of the Trustee) connected therewith.

                 Every new Security issued, authenticated and delivered by the
Trustee pursuant to this Section 3.06 in lieu of any destroyed, lost or stolen
Security shall constitute an original additional contractual obligation of the
Company, whether or not the destroyed, lost or stolen Security shall be at any
time enforceable by anyone, and shall be entitled to all the benefits of this
Indenture equally and proportionately with any and all other Securities duly
issued hereunder.

                 The provisions of this Section are exclusive and shall
preclude (to the extent lawful) all other rights and remedies with respect to
the replacement or payment of mutilated, destroyed, lost or stolen Securities.

                 SECTION 3.07.  Payment of Interest; Interest Rights Preserved.
Interest on any Security which is payable, and is punctually paid or duly
provided for, on any
<PAGE>   38
                                                                              32




Interest Payment Date shall be paid to the Person in whose name that Security
(or one or more Predecessor Securities) is registered at the close of business
on the Regular Record Date for payment of such interest.

                 If the Company shall be required by law to deduct any taxes
from any sum of interest payable hereunder to a Holder, (i) the Company shall
make such deductions and shall pay the full amount deducted to the relevant
taxing authority in accordance with applicable law and (ii) the amount of such
deduction shall be treated for purposes hereof as a payment of interest.

                 Any interest on any Security which is payable, but is not
punctually paid or duly provided for, on any Interest Payment Date (herein
called "Defaulted Interest") shall forthwith cease to be payable to the Holder
on the relevant Regular Record Date by virtue of having been such Holder, and
such Defaulted Interest may be paid by the Company, at its election in each
case, as provided in clause (1) or (2) below:

                 (1) The Company may elect to make payment of any Defaulted
     Interest to the Persons in whose names the Securities (or their respective
     Predecessor Securities) are registered at the close of business on a
     Special Record Date for the payment of such Defaulted Interest, which
     shall be fixed in the following manner.  The Company shall notify the
     Trustee in writing of the amount of Defaulted Interest proposed to be paid
     on each Security and the date of the proposed payment, and at the same
     time the Company shall deposit with the Trustee an amount of money equal
     to the aggregate amount proposed to be paid in respect of such Defaulted
     Interest or shall make arrangements satisfactory to the Trustee for such
     deposit prior to the date of the proposed payment, such money when
     deposited to be held in trust for the benefit of the Persons entitled to
     such Defaulted Interest as in this clause (1) provided.  Thereupon, the
     Trustee shall fix a Special Record Date for the payment of such Defaulted
     Interest which shall be not more than 15 days and not less than 10 days
     prior to the date of the proposed payment and not less than 10 days after
     the receipt by the Trustee of the notice of the proposed payment.  The
     Trustee shall promptly notify the Company of such Special Record Date and,
     in the name and at the expense of the Company, shall cause notice of the
     proposed payment of such Defaulted Interest and the Special Record Date
     therefor to be mailed, first-class postage prepaid, to each Holder at his
     address as it appears in the Security Register, not less than 10 days
     prior to such Special Record Date.  Notice of the proposed payment of such
     Defaulted Interest and the Special Record Date therefor having been so
     mailed, such Defaulted Interest shall be paid to the Persons in whose
     names the Securities (or their respective Predecessor Securities) are
     registered at the close of business on such Special Record Date and shall
     no longer be payable pursuant to the following clause (2).

                 (2) The Company may make payment of any Defaulted Interest in
     any other lawful manner not inconsistent with the requirements of any
     securities exchange on which the Securities may be listed, and upon such
     notice as may be required by such exchange, if, after notice given by the
     Company to the Trustee of the proposed payment pursuant to this clause
     (2), such manner of payment shall be deemed practicable by the Trustee.

                 Subject to the foregoing provisions of this Section, each
Security delivered under this Indenture upon registration of transfer of or in
exchange for or in lieu of any
<PAGE>   39
                                                                              33




other Security shall carry the rights to interest accrued and unpaid, and to
accrue, which were carried by such other Security.

                 In the case of any Security which is converted after any
Regular Record Date and on or prior to the corresponding Interest Payment Date,
interest on such Security whose Stated Maturity is on such Interest Payment
Date shall be deemed to continue to accrue and shall be payable on such
Interest Payment Date notwithstanding such conversion and notwithstanding that
such Security may have been called for redemption on a Redemption Date within
such period, and such interest (whether or not punctually paid or duly provided
for) shall be paid to the Person in whose name that Security (or one or more
Predecessor Securities) is registered at the close of business on such Regular
Record Date.  Except as otherwise expressly provided in the immediately
preceding sentence, in the case of any Security which is converted, interest
whose Stated Maturity is after the date of conversion of such Security shall
not be payable.

                 SECTION 3.08.  Persons Deemed Owners.  Prior to due
presentment of a Security for registration of transfer, the Company, the
Trustee and any agent of the Company or the Trustee may treat the Person in
whose name such Security is registered as the owner of such Security for the
purpose of receiving payment of principal of, premium, if any (including the
Make-Whole Payment, if any), and (subject to Section 3.07) interest on such
Security and for all other purposes whatsoever, whether or not such Security be
overdue, and neither the Company, the Trustee nor any agent of the Company or
the Trustee shall be affected by notice to the contrary.

                 SECTION 3.09.  Cancellation.  All Securities surrendered for
payment, redemption, repurchase, registration of transfer or exchange or
conversion shall, if surrendered to any Person other than the Trustee, be
delivered to the Trustee and shall be promptly cancelled by it.  The Company
may at any time deliver to the Trustee for cancellation any Securities
previously authenticated and delivered hereunder which the Company may have
acquired in any manner whatsoever, and all Securities so delivered shall be
promptly cancelled by the Trustee.  No Securities shall be authenticated in
lieu of or in exchange for any Securities cancelled as provided in this
Section, except as expressly permitted by this Indenture.  All cancelled
Securities held by the Trustee shall be disposed of as directed by a Company
Order; provided however, the Trustee shall not be required to destroy such
cancelled Securities..

                 SECTION 3.10.  Computation of Interest.  Interest on the
Securities shall be computed on the basis of a 360-day year of twelve 30-day
months.


                                   ARTICLE IV

                           Satisfaction and Discharge

                 SECTION 4.01.  Satisfaction and Discharge of Indenture.  This
Indenture shall upon Company request cease to be of further effect (except as
to any surviving rights of conversion, registration of transfer or exchange of
Securities herein expressly provided for), and the Trustee, at the expense of
the Company, shall execute proper instruments acknowledging satisfaction and
discharge of this Indenture, when
<PAGE>   40
                                                                              34




                 (1)  either

                          (A) all Securities theretofore authenticated and
                 delivered (other than (i) Securities which have been
                 destroyed, lost or stolen and which have been replaced or paid
                 as provided in Section 3.06 and (ii) Securities for whose
                 payment money has theretofore been deposited in trust or
                 segregated and held in trust by the Company and thereafter
                 repaid to the Company or discharged from such trust, as
                 provided in Section 10.03) have been delivered to the Trustee
                 for cancellation;

                          (B) all such Securities not theretofore delivered to
             the Trustee for cancellation

                   (i)     have become due and payable, or

                   (ii)    will become due and payable at their Stated Maturity
             within one year,
                                      or

                 (iii)     are to be called for redemption within one year under
             arrangements satisfactory to the Trusteefor the giving of notice
             of redemption by the Trustee in the name, and at the expense, of
             the Company,

and the Company, in the case of (i), (ii) or (iii) above, has deposited or
caused to be deposited irrevocably with the Trustee as trust funds in trust for
the benefit of Holders of Outstanding Securities in an amount sufficient to pay
and discharge the entire indebtedness on such Securities not theretofore
delivered to the Trustee for cancellation, for principal and premium, if any
(including the Make-Whole Payment, if any), and interest to the date of such
deposit (in the case of Securities which have become due and payable) or to the
Stated Maturity or Redemption Date, as the case may be;

                 (2)  the Company has paid or caused to be paid all other sums
     payable hereunder by the Company;

                 (3)  the Company has delivered to the Trustee an Officers'
     Certificate and an Opinion of Counsel, each stating that all conditions
     precedent herein provided for relating to the satisfaction and discharge
     of this Indenture have been complied with; and

                 (4)  no Event of Default which, with notice or lapse of time,
     or both, would become an Event of Default with respect to the Securities
     shall have occurred and be continuing on the date of such deposit.

Notwithstanding the satisfaction and discharge of this Indenture, the
obligations of the Company to the Trustee under Section 6.07, the obligations
of the Company to any Authenticating Agent under Section 6.14 and, if money
shall have been deposited with the Trustee pursuant to subclause (B) of clause
(1) of this Section, the obligations of the Trustee under Section 4.02 and the
last paragraph of Section 10.03 shall survive.

                 SECTION 4.02.  Application of Trust Money.  Subject to the
provisions of the last paragraph of Section 10.03, all money deposited with the
Trustee pursuant to Section 4.01 shall be held in trust and applied by it, in
accordance with the provisions of
<PAGE>   41
                                                                              35




the Securities and this Indenture, to the payment, either directly or through
any Paying Agent (including the Company acting as its own Paying Agent) as the
Trustee may determine, to the Persons entitled thereto, of the principal and
premium, if any (including the Make-Whole Payment, if any), and interest for
whose payment such money has been deposited with the Trustee.  All moneys
deposited with the Trustee pursuant to Section 4.01 (and held by it or any
Paying Agent) for the payment of Securities subsequently converted shall be
returned to the Company upon Company Request.


                                   ARTICLE V

                                    Remedies

                 SECTION 5.01.  Events of Default.  "Event of Default",
wherever used herein, means any one of the following events (whatever the
reason for such Event of Default and whether it shall be occasioned by the
provisions of Article XII or be voluntary or involuntary or be effected by
operation of law or pursuant to any judgment, decree or order of any court or
any order, rule or regulation of any administrative or governmental body):

                 (1)  default in the payment of any interest (including
     Additional Interest) upon any Security when it becomes due and payable,
     and continuance of such default for a period of 30 days (whether or not
     such payment is prohibited by the provisions of Article XII); or

                 (2)  default in the payment of the principal of or premium, if
     any (including the Make-Whole Payment, if any), on any Security at its
     Maturity (whether or not such payment is prohibited by the provisions of
     Article XII); or

                 (3)  failure by the Company to provide the notice of a Change
     in Control in accordance with Section 14.02 or notice of a Change in
     Control or default in the payment of the Repurchase Price in respect of
     any Security on the Repurchase Date therefor (whether or not such payment
     is prohibited by the provisions of Article XII); or

                 (4)  default in the performance, or breach, of any covenant or
     warranty of the Company in this Indenture (other than a covenant or
     warranty a default in whose performance or whose breach is elsewhere in
     this Section specifically dealt with), and continuance of such default or
     breach for a period of 60 days after there has been given, by registered
     or certified mail, to the Company by the Trustee or to the Company and the
     Trustee by the Holders of at least 25% in principal amount of the
     Outstanding Securities a written notice specifying such default or breach
     and requiring it to be remedied and stating that such notice is a "Notice
     of Default" hereunder: or

                 (5)  a default under any bonds, debentures, notes or other
     evidences of indebtedness for money borrowed by the Company or a
     Subsidiary or under any mortgages, indentures or instruments under which
     there may be issued or by which there may be secured or evidenced any
     indebtedness for money borrowed by the Company or a Subsidiary, whether
     such indebtedness now exists or shall hereafter be created, other than
     under a Non-Recourse Obligation, which indebtedness,
<PAGE>   42
                                                                              36




     individually or in the aggregate, has a principal amount outstanding in
     excess of U.S.$10,000,000, which default shall constitute a failure to pay
     any portion of the principal of such indebtedness when due and payable
     after the expiration of any applicable grace or cure period with respect
     thereto or shall have resulted in such indebtedness becoming or being
     declared due and payable prior to the date on which it would otherwise
     have become due and payable, without such indebtedness having been
     discharged, or such acceleration having been rescinded or annulled, within
     a period of 10 days after there shall have been given, by registered or
     certified mail, to the Company by the Trustee or to the Company and the
     Trustee by the Holders of at least 25% in principal amount of the
     Outstanding Securities a written notice specifying such default and
     requiring the Company to cause such indebtedness to be discharged or cause
     such acceleration to be rescinded or annulled and stating that such notice
     is a "Notice of Default" hereunder; or

                 (6)  the entry by a court having jurisdiction in the premises
     of (A) a decree or order for relief in respect of the Company or a
     Subsidiary in an involuntary case or proceeding under any applicable
     Federal or State bankruptcy, insolvency, reorganization or other similar
     law or (B) a decree or order adjudging the Company or a Subsidiary
     bankrupt or insolvent, or approving as properly filed a petition seeking
     reorganization, arrangement, adjustment or composition of or in respect of
     the Company or a Subsidiary under any applicable Federal or State law, or
     appointing a custodian, receiver, liquidator, assignee, trustee,
     sequestrator or other similar official of the Company or a Subsidiary or
     of any substantial part of their respective properties, or ordering the
     winding up or liquidation of the affairs of the Company or a Subsidiary,
     and the continuance of any such decree or order for relief or any such
     other decree or order unstayed and in effect for a period of 60
     consecutive days; or

                 (7)  the commencement by the Company or a Subsidiary of a
     voluntary case or proceeding under any applicable Federal or State
     bankruptcy, insolvency, reorganization or other similar law or of any
     other case or proceeding to be adjudicated a bankrupt or insolvent, or the
     consent by either the Company or a Subsidiary to the entry of a decree or
     order for relief in respect of the Company or a Subsidiary in an
     involuntary case or proceeding under any applicable Federal or State
     bankruptcy, insolvency, reorganization or other similar law or to the
     commencement of any bankruptcy or insolvency case or proceeding against
     either the Company or a Subsidiary, or the filing by either the Company or
     a Subsidiary of a petition or answer or consent seeking reorganization or
     relief under any applicable Federal or State law, or the consent by either
     the Company or a Subsidiary to the filing of such petition or to the
     appointment of or taking possession by a custodian, receiver, liquidator,
     assignee, trustee, sequestrator or other similar official of the Company
     or a Subsidiary or of any substantial part of their respective properties,
     or the making by either the Company or a Subsidiary of an assignment for
     the benefit of creditors, or the admission by either the Company or a
     Subsidiary in writing of an inability to pay the debts of either the
     Company or a Subsidiary generally as they become due, or the taking of
     corporate action by the Company or a Subsidiary in furtherance of any such
     action.

                 SECTION 5.02.  Acceleration of Maturity; Rescission and
Annulment.  If an Event of Default (other than an Event of Default specified in
Section 5.01(l), 5.01(2), 5.01(6) or 5.01(7)) occurs and is continuing, then in
every such case the Trustee or the
<PAGE>   43
                                                                              37




Holders of not less than 25% in principal amount of the Outstanding Securities
may declare the principal of all the Securities to be due and payable
immediately, by a notice in writing to the Company (and to the Trustee if given
by Holders), and upon any such declaration such principal and any accrued
interest (including Additional Interest) thereon shall become immediately due
and payable.  If an Event of Default specified in Section 5.01(6) or 5.01(7)
occurs, the principal of, and accrued interest (including Additional Interest)
on, all the Securities shall automatically, and without any declaration or
other action on the part of the Trustee or any Holder, become immediately due
and payable.

                 At any time after such a declaration of acceleration has been
made and before a judgment or decree for payment of the money due has been
obtained by the Trustee as hereinafter in this Article V provided, the Holders
of a majority in principal amount of the Outstanding Securities, by written
notice to the Company and the Trustee, may rescind and annul such declaration
and its consequences if

                 (1) the Company has paid or deposited with the Trustee a sum
     sufficient to pay

                          (A) all overdue interest (including Additional
                 Interest) on all Securities,

                          (B) the principal of and premium, if any (including
                 the Make-Whole Payment, if any), on any Securities which have
                 become due otherwise than by such declaration of acceleration
                 and interest thereon at the rate borne by the Securities,

                          (C) to the extent that payment of such interest is
                 lawful, interest upon overdue interest at the rate borne by
                 the Securities, and

                          (D) all sums paid or advanced by the Trustee
                 hereunder and the reasonable compensation, expenses,
                 disbursements and advances of the Trustee, its agents and
                 counsel;

     and

                 (2) all Events of Default, other than the nonpayment of the
     principal of Securities which have become due solely by such declaration
     of acceleration, have been cured or waived as provided in Section 5.13.

No such rescission shall affect any subsequent default or impair any right
consequent thereon.

                 SECTION 5.03. Collection of Indebtedness and Suits for
Enforcement by Trustee. If

                 (1) default is made in the payment of any interest on any
     Security when such interest becomes due and payable and such default
     continues for a period of 30 days, or
<PAGE>   44
                                                                              38




                 (2) default is made in the payment of the principal of or
     premium, if any (including the Make-Whole Payment, if any), on any
     Security at the Maturity thereof,

the Trustee is authorized to recover judgment in its own name and as trustee of
an express trust against the Company for the whole amount then due and payable
on such Securities for principal and premium, if any (including the Make-Whole
Payment, if any), and interest, and, to the extent that payment of such
interest shall be legally enforceable, interest on any overdue principal and
premium, if any (including the Make-Whole Payment, if any), and on any overdue
interest, at the rate borne by the Securities, and, in addition thereto, such
further amount as shall be sufficient to cover the costs and expenses of
collection, including the reasonable compensation, expenses, disbursements and
advances of the Trustee, its agents and counsel.

                 If an Event of Default occurs and is continuing, the Trustee
may in its discretion proceed to protect and enforce its rights and the rights
of the Holders by such appropriate judicial proceedings as the Trustee shall
deem most effectual to protect and enforce any such rights, whether for the
specific enforcement of any covenant or agreement in this Indenture or in aid
of the exercise of any power granted herein, or to enforce any other proper
remedy.

                 SECTION 5.04.  Trustee May File Proofs of Claim.  In case of
any judicial proceeding relative to the Company (or any other obligor upon the
Securities), its property or its creditors, the Trustee shall be entitled and
empowered, by intervention in such proceeding or otherwise,

                 (1) to file and prove a claim for the whole amount of
     principal and interest owing and unpaid in respect of the Securities and
     to file such other papers or documents as may be necessary or advisable in
     order to have the claims of the Trustee (including any claim for the
     reasonable compensation, expenses, disbursements and advances of the
     Trustee, its agents and counsel) and of the Holders allowed in such
     judicial proceeding, and

                 (2) to collect and receive any moneys or other property
     payable or deliverable on any such claim and to distribute the same;

and any custodian, receiver, assignee, trustee, liquidator, sequestrator or
other similar official in any such judicial proceeding is hereby authorized by
each Holder to make such payments to the Trustee and, in the event that the
Trustee shall consent to the making of such payments directly to the Holders,
to pay to the Trustee any amount due it for the reasonable compensation,
expenses, disbursements and advances of the Trustee, its agents and counsel,
and any other amounts due the Trustee under Section 6.07.

                 No provision of this Indenture shall be deemed to authorize
the Trustee to authorize or consent to or accept or adopt on behalf of any
Holder any plan of reorganization, arrangement, adjustment or composition
affecting the Securities or the rights of any Holder thereof or to authorize
the Trustee to vote in respect of the claim of any Holder in any such
proceeding; provided, however, that the Trustee may, on behalf of the Holders,
vote for the election of a trustee in bankruptcy or similar official and be a
member of a creditors' or other similar committee.
<PAGE>   45
                                                                              39




                 SECTION 5.05.  Trustee May Enforce Claims Without Possession
of Securities.  All rights of action and claims under this Indenture or the
Securities may be prosecuted and enforced by the Trustee without the possession
of any of the Securities or the production thereof in any proceeding relating
thereto, and any such proceeding instituted by the Trustee shall be brought in
its own name as trustee of an express trust, and any recovery of judgment
shall, after provision for the payment of the reasonable compensation,
expenses, disbursements and advances of the Trustee, its agents and counsel, be
for the ratable benefit of the Holders of the Securities in respect of which
such judgment has been recovered.

                 SECTION 5.06.  Application of Money Collected.  Any money
collected by the Trustee pursuant to this Article V shall be applied in the
following order, at the date or dates fixed by the Trustee and, in case of the
distribution of such money on account of principal or premium, if any
(including the Make-Whole Payment, if any), or interest, upon presentation of
the Securities and the notation thereon of the payment if only partially paid
and upon surrender thereof if fully paid:

                 FIRST:  to the payment of all amounts due the Trustee under
Section 6.07;

                 SECOND:  subject to Article XII, to the payment of the amounts
     then due and unpaid for first, interest (including Additional Interest)
     on, and, second, for principal of and premium, if any (including the
     Make-Whole Payment, if any), on the Securities in respect of which or for
     the benefit of which such money has been collected, ratably, without
     preference or priority of any kind, according to the amounts due and
     payable on such Securities for interest and principal and premium, if any
     (including the Make-Whole Payment, if any), respectively;

                 THIRD:  the balance, if any, to the Person or Persons entitled
     thereto, as their interest may appear or as a court of competent
     jurisdiction shall direct; and

                 FOURTH:  to the Company.

                 SECTION 5.07.  Limitation on Suits.  No Holder of any Security
shall have any right to institute any proceeding, judicial or otherwise, with
respect to this Indenture, or for the appointment of a receiver or trustee, or
for any other remedy hereunder, unless

                 (1) such Holder has previously given written notice to a
     Responsible Officer the Trustee of a continuing Event of Default;

                 (2) the Holders of not less than 25% in principal amount of
     the Outstanding Securities shall have made written request to the Trustee
     to institute proceedings in respect of such Event of Default in its own
     name as Trustee hereunder;

                 (3) such Holder or Holders have offered to the Trustee
     indemnity satisfactory to it (which indemnity shall not be unreasonable)
     against the costs, expenses and liabilities to be incurred in compliance
     with such request;

                 (4) the Trustee for 60 days after its receipt of such notice,
     request and offer of indemnity has failed to institute any such
     proceeding; and
<PAGE>   46
                                                                              40




                 (5) no direction inconsistent with such written request has
     been given to the Trustee during such 60-day period by the Holders of a
     majority in principal amount of the Outstanding Securities;

it being understood and intended that no one or more of such Holders shall have
any right in any manner whatever by virtue of, or by availing of, any provision
of this Indenture to affect, disturb or prejudice the fights of any other of
such Holders, or to obtain or to seek to obtain priority or preference over any
other of such Holders or to enforce any right under this Indenture, except in
the manner herein provided and for the equal and ratable benefit of all of such
Holders.

                 SECTION 5.08.  Unconditional Right of Holders To Receive
Principal, Premium and Interest and To Convert.  Notwithstanding any other
provision in this Indenture, the Holder of any Security shall have the right,
which is absolute and unconditional, to receive payment of the principal of and
premium, if any (including the Make-Whole Payment, if any), and (subject to
Section 3.07) interest on such Security on the respective Stated Maturities
expressed in such Security (or, in the case of redemption or repurchase, on the
Redemption Date or Repurchase Date, as the case may be) and to convert such
Security in accordance with Article XIII and to institute suit for the
enforcement of any such payment and right to convert, and such rights shall not
be impaired without the consent of such Holder.

                 SECTION 5.09.  Restoration of Rights and Remedies. If the
Trustee or any Holder has instituted any proceeding to enforce any right or
remedy under this Indenture and such proceeding has been discontinued or
abandoned for any reason, or has been determined adversely to the Trustee or to
such Holder, then and in every such case, subject to any determination in such
proceeding, the Company, the Trustee and the Holders shall be restored
severally and respectively to their former positions hereunder and thereafter
all rights and remedies of the Trustee and the Holders shall continue as though
no such proceeding had been instituted.

                 SECTION 5.10.  Rights and Remedies Cumulative. Except as
otherwise provided with respect to the replacement or payment of mutilated,
destroyed, lost or stolen Securities in the last paragraph of Section 3.06, no
right or remedy herein conferred upon or reserved to the Trustee or to the
Holders is intended to be exclusive of any other right or remedy, and every
right and remedy shall, to the extent permitted by law, be cumulative and in
addition to every other right and remedy given hereunder or now or hereafter
existing at law or in equity or otherwise.  The assertion or employment of any
right or remedy hereunder, or otherwise, shall not prevent the concurrent
assertion or employment of any other appropriate right or remedy.

                 SECTION 5.11.  Delay or Omission Not Waiver.  No delay or
omission of the Trustee or of any Holder of any Securities to exercise any
right or remedy accruing upon any Event of Default shall impair any such right
or remedy or constitute a waiver of any such Event of Default or an
acquiescence therein.  Every right and remedy given by this Article V or by law
to the Trustee or to the Holders may be exercised from time to time, and as
often as may be deemed expedient, by the Trustee or by the Holders, as the case
may be.

                 SECTION 5.12.  Control by Holders.  The Holders of a majority
in principal amount of the Outstanding Securities shall have the right to
direct the time,
<PAGE>   47
                                                                              41




method and place of conducting any proceeding for any remedy available to the
Trustee or exercising any trust or power conferred on the Trustee; provided
that

                 (1) such direction shall not be in conflict with any rule of
     law or with this Indenture, and

                 (2) the Trustee may take any other action deemed proper by the
     Trustee which is not inconsistent with such direction.

                 SECTION 5.13.  Waiver of Past Defaults.  The Holders of not
less than a majority in principal amount of the Outstanding Securities may on
behalf of the Holders of all the Securities waive any past default hereunder
and its consequences, except a default

                 (1) in the payment of the principal of or premium, if any
     (including the Make-Whole Payment, if any), or interest on any Security,
     or

                 (2) in respect of a covenant or provision hereof which under
     Article IX cannot be modified or amended without the consent of the Holder
     of each Outstanding Security affected.

                 Upon any such waiver, such default shall cease to exist, and
any Event of Default arising therefrom shall be deemed to have been cured, for
every purpose of this Indenture; but no such waiver shall extend to any
subsequent or other default or impair any right consequent thereon.

                 SECTION 5.14. Undertaking for Costs.  In any suit for the
enforcement of any right or remedy under this Indenture, or in any suit against
the Trustee for any action taken, suffered or omitted by it as Trustee, a court
may require any party litigant in such suit to file an undertaking to pay the
costs of such suit, and may assess costs against any such party litigant,
having due regard to the merits and good faith of the claims or defenses made
by such party litigant; provided, that this Section 5.14 shall not be deemed to
authorize any court to require such an undertaking or to make such an
assessment in any suit instituted by the Trustee or the Company or in any suit
for the enforcement of the right to convert any Security in accordance with
Article XIII.

                 SECTION 5.15.  Waiver of Usury, Stay or Extension Laws.  The
Company covenants (to the extent that it may lawfully do so) that it will not
at any time insist upon, or plead, or in any manner whatsoever claim or take
the benefit or advantage of, any usury, stay or extension law wherever enacted,
now or at any time hereafter in force, which may affect the covenants or the
performance of this Indenture; and the Company (to the extent that it may
lawfully do so) hereby expressly waives all benefit or advantage of any such
law and covenants that it will not hinder, delay or impede the execution of any
power herein granted to the Trustee, but will suffer and permit the execution
of every such power as though no such law had been enacted.
<PAGE>   48
                                                                              42



                                   ARTICLE VI

                                  The Trustee

                 SECTION 6.01. Certain Duties and Responsibilities.  (a)
Except during the continuance of an Event of Default,

                 (1) the Trustee undertakes to perform such duties and only
     such duties as are specifically set forth in this Indenture, and no
     implied covenants or obligations shall be read into this Indenture against
     the Trustee; and

                 (2) in the absence of bad faith on its part, the Trustee may
     conclusively rely, as to the truth of the statements and the correctness
     of the opinions expressed therein, upon certificates or opinions furnished
     to the Trustee and conforming to the requirements of this Indenture; but
     in the case of any such certificates or opinions which by any provision
     hereof are specifically required to be furnished to the Trustee, the
     Trustee shall be under a duty to examine the same to determine whether or
     not they conform to the requirements of this Indenture.

                 (b)  In case an Event of Default has occurred and is
continuing, the Trustee shall exercise such of the rights and powers vested in
it by this Indenture, and use the same degree of care and skill in their
exercise, as a prudent person would exercise or use under the circumstances in
the conduct of his or her own affairs.

                 (c)  No provision of this Indenture shall be construed to
relieve the Trustee from liability for its own negligent action, its own
negligent failure to act, or its own willful misconduct, except that

                 (1) this paragraph (c) shall not be construed to limit the
     effect of paragraph (a) of this Section;

                 (2) the Trustee shall not be liable for any error of judgment
     made in good faith by a Responsible Officer, unless it shall be proved
     that the Trustee was negligent in ascertaining the pertinent facts;

                 (3) the Trustee shall not be liable with respect to any action
     taken or omitted to be taken by it in good faith in accordance with the
     direction of the Holders of a majority in principal amount of the
     Outstanding Securities relating to the time, method and place of
     conducting any proceeding for any remedy available to the Trustee, or
     exercising any trust or power conferred upon the Trustee, under this
     Indenture; and

                 (4) no provision of this Indenture shall require the Trustee
     to expend or risk its own funds or otherwise incur any financial liability
     in the performance of any of its duties hereunder, or in the exercise of
     any of its rights or powers.

                 (d)  Whether or not therein expressly so provided, every
provision of this Indenture relating to the conduct or affecting the liability
of or affording protection to the Trustee (as Trustee, Paying Agent,
Authenticating Agent or Security Registrar) shall be subject to the provisions
of this Section.
<PAGE>   49
                                                                              43



                 SECTION 6.02.  Notice of Defaults.  Within 90 days after the
occurrence of any default hereunder, the Trustee shall give the Holders, in the
manner provided in Section 1.06, notice of any default hereunder actually known
to a Responsible Officer of the Trustee; provided, however, that in the case of
any default of the character specified in Section 5.01(3), no such notice to
Holders shall be given until at least 30 days after the occurrence thereof.
The Trustee shall not be deemed to have notice of a default unless (i) the
Trustee has received written notice thereof from the Company or any Holder or
(ii) a Responsible Officer of the Trustee shall have actual knowledge thereof.
For the purpose of this Section, the term "default" means any event which is,
or after notice or lapse of time or both would become, an Event of Default.

                 SECTION 6.03.  Certain Rights of Trustee.  Subject to the
provisions of Section 6.01:

                 (a) the Trustee may conclusively rely and shall be protected
     in acting or refraining from acting upon any resolution, certificate,
     statement, instrument, opinion, report, notice, request, direction,
     consent, order, bond, debenture, note, other evidence of indebtedness or
     other paper or document believed by it to be genuine and to have been
     signed or presented by the proper party or parties;

                 (b) any request or direction of the Company mentioned herein
     shall be sufficiently evidenced by a Company Request or Company Order and
     any resolution of the Board of Directors shall be sufficiently evidenced
     by a Board Resolution;

                 (c) whenever in the administration of this Indenture the
     Trustee shall deem it desirable that a matter be proved or established
     prior to taking, suffering or omitting any action hereunder, the Trustee
     (unless other evidence be herein specifically prescribed) may require and,
     in the absence of bad faith on its part, conclusively rely upon an
     Officers' Certificate;

                 (d) the Trustee may consult with counsel of its selection and
     the advice of such counsel or any Opinion of Counsel shall be full and
     complete authorization and protection in respect of any action taken,
     suffered or omitted by it hereunder in good faith and in reliance thereon;

                 (e) the Trustee shall be under no obligation to exercise any
     of the rights or powers vested in it by this Indenture at the request or
     direction of any of the Holders pursuant to this Indenture, unless such
     Holders shall have offered to the Trustee security or indemnity
     satisfactory to the Trustee (which security or indemnity shall not be
     unreasonable) against the costs, expenses and liabilities which might be
     incurred by it in compliance with such request or direction;

                 (f) the Trustee shall not be bound to make any investigation
     into the facts or matters stated in any resolution, certificate,
     statement, instrument, opinion, report, notice, request, direction,
     consent, order, bond, debenture, note, other evidence of indebtedness or
     other paper or document, but the Trustee, in its discretion, may make such
     further inquiry or investigation into such facts or matters as it may see
     fit, and, if the Trustee shall determine to make such further inquiry or
     investigation, it shall be entitled to examine the books, records and
     premises of the Company, personally or by agent or attorney; and
<PAGE>   50
                                                                              44




                 (g) the Trustee may execute any of the trusts or powers
     hereunder or perform any duties hereunder either directly or by or through
     agents or attorneys and the Trustee shall not be responsible for any
     misconduct or negligence on the part of any agent or attorney appointed
     with due care by it hereunder.

                 (h) no provision of this Indenture shall require the Trustee
     to expend or risk its own funds or otherwise incur any financial liability
     in the performance of any of its duties hereunder, or in the exercise of
     any of its rights or powers.

                 SECTION 6.04.  Not Responsible for Recitals or Issuance of
Securities.  The recitals contained herein and in the Securities, except the
Trustee's certificates of authentication, shall be taken as the statements of
the Company, and neither the Trustee nor any Authenticating Agent assumes any
responsibility for their correctness.  The Trustee makes no representations as
to the validity or sufficiency of this Indenture or of the Securities.  Neither
the Trustee nor any Authenticating Agent shall be accountable for the use or
application by the Company of Securities or the proceeds thereof.

                 SECTION 6.05.  May Hold Securities.  The Trustee, any
Authenticating Agent, any Paying Agent, any Security Registrar or any other
agent of the Company, in its individual or any other capacity, may become the
owner or pledgee of Securities and, subject to Section 6.08 and Section 6.13,
may otherwise deal with the Company with the same rights it would have if it
were not Trustee, Authenticating Agent, Paying Agent, Security Registrar or
such other agent.

                 SECTION 6.06.  Money Held in Trust.  Money held by the Trustee
in trust hereunder need not be segregated from other funds except to the extent
required by law.  The Trustee shall be under no liability for interest on any
money received by it hereunder except as otherwise agreed with the Company in
writing.

                 SECTION 6.07.  Compensation and Reimbursement.  The Company
agrees:

                 (1) to pay to the Trustee from time to time such compensation
     as shall be agreed in writing between the Company and the Trustee for all
     services rendered by it hereunder (which compensation shall not be limited
     by any provision of law in regard to the compensation of a trustee of an
     express trust);

                 (2) except as otherwise expressly provided herein, to
     reimburse the Trustee upon its request for all reasonable expenses,
     disbursements and advances incurred or made by the Trustee in accordance
     with any provision of this Indenture (including the reasonable
     compensation and the expenses and disbursements of its agents and
     counsel), except any such expense, disbursement or advance as may be
     attributable to its negligence or willful misconduct;

                 (3) to indemnify the Trustee for, and to hold it harmless
     against, any loss, liability or expense incurred without negligence or
     willful misconduct on its part, arising out of or in connection with the
     acceptance or administration of this trust, including the costs and
     expenses of defending itself against any claim (whether asserted by the
     Company, a Holder of Securities or any other Person) or liability in
     connection with the exercise or performance of any of its powers or duties
     hereunder.
<PAGE>   51
                                                                              45




     The Trustee shall notify the Company of any claim asserted against it for
     which it may seek indemnity;

                 (4)  all indemnifications and releases from liability granted
     hereunder to the Trustee shall extend to its officers, directors,
     employees, agents, successors and assigns;

                 (5)  when the Trustee incurs expenses or renders services
     after the occurrence of any Event of Default specified in Section 5.01,
     the expenses and the compensation for the services are intended to
     constitute expenses of administration under any bankruptcy, insolvency or
     similar laws; and

                 (6)  the obligations of the Company under this Section shall
     survive the satisfaction and discharge of this Indenture.

                 SECTION 6.08.  Disqualification; Conflicting Interests.  If
the Trustee has or shall acquire a conflicting interest within the meaning of
the Trust Indenture Act, the Trustee shall either eliminate such interest or
resign, to the extent and in the manner provided by, and subject to the
provisions of, the Trust Indenture Act and this Indenture.

                 SECTION 6.09.  Corporate Trustee Required; Eligibility.  There
shall at all times be a Trustee hereunder which shall be a corporation
organized and doing business under the laws of the United States, authorized
under such laws to exercise corporate trust powers, which shall have (or, in
the case of a corporation included in a bank holding company system, the
related bank holding company shall have) a combined capital and surplus of at
least U.S.$50,000,000, subject to supervision or examination by Federal or
State authority, in good standing and having an established place of business
or agency in the Borough of Manhattan, The City of New York.  If such
corporation or related bank holding company publishes reports of condition at
least annually, pursuant to law or to the requirements of said supervising or
examining authority, then for the purposes of this Section, the combined
capital and surplus of such corporation or related bank holding company shall
be deemed to be its combined capital and surplus as set forth in its most
recent report of condition so published.  If at any time the Trustee shall
cease to be eligible in accordance with the provisions of this Section, it
shall resign immediately in the manner and with the effect hereinafter
specified in this Article VI.

                 SECTION 6.10.  Resignation and Removal; Appointment of
Successor. (a)  No resignation or removal of the Trustee and no appointment of
a successor Trustee pursuant to this Article shall become effective until the
acceptance of appointment by the successor Trustee in accordance with the
applicable requirements of Section 6.11.

                 (b)  The Trustee may resign at any time by giving written
notice thereof to the Company.  If the instrument of acceptance by a successor
Trustee required by Section 6.11 shall not have been delivered to the Trustee
within 30 days after the giving of such notice of resignation, the resigning
Trustee may petition any court of competent jurisdiction for the appointment of
a successor Trustee.

                 (c)  The Trustee may be removed at any time by Act of the
Holders of a majority in principal amount of the Outstanding Securities,
delivered to the Trustee and to the Company.  If the instrument of acceptance
by a successor Trustee required by Section 6.11 shall not have been delivered
to the Trustee within 30 days after the giving
<PAGE>   52
                                                                              46




of such notice of resignation, the resigning Trustee may petition any court of
competent jurisdiction for the appointment of a successor Trustee.

                 (d)  If at any time:

                 (1)  the Trustee shall fail to comply with Section 6.08 after
     written request therefor by the Company or by any Holder who has been a
     bona fide Holder of a Security for at least six months, or

                 (2)  the Trustee shall cease to be eligible under Section 6.09
     and shall fail to resign after written request therefor by the Company or
     by any such Holder, or

                 (3)  the Trustee shall become incapable of acting or shall be
     adjudged a bankrupt or insolvent or a receiver of the Trustee or of its
     property shall be appointed or any public officer shall take charge or
     control of the Trustee or of its property or affairs for the purpose of
     rehabilitation, conservation or liquidation,

then, in any such case, (i) the Company by a Board Resolution may remove the
Trustee, or (ii) subject to Section 5.14, any Holder who has been a bona fide
Holder of a Security for at least six months may, on behalf of himself and all
others similarly situated, petition any court of competent jurisdiction for the
removal of the Trustee and the appointment of a successor Trustee.

                 (e)  If the Trustee shall resign, be removed or become
incapable of acting, or if a vacancy shall occur in the office of Trustee for
any cause, the Company, by a Board Resolution, shall promptly appoint a
successor Trustee.  If, within one year after such resignation, removal or
incapability, or the occurrence of such vacancy, a successor Trustee shall be
appointed by Act of the Holders of a majority in principal amount of the
Outstanding Securities delivered to the Company and the retiring Trustee, the
successor Trustee so appointed shall, forthwith upon its acceptance of such
appointment in accordance with the applicable requirements of Section 6.11,
become the successor Trustee and to that extent supersede the successor Trustee
appointed by the Company.  If no successor Trustee shall have been so appointed
by the Company or the Holders and accepted appointment in the manner required
by Section 6.11, any Holder who has been a bona fide Holder of a Security for
at least six months may, on behalf of himself and all others similarly
situated, petition any court of competent jurisdiction for the appointment of a
successor Trustee.

                 (f)  The Company shall give notice of each resignation and
each removal of the Trustee and each appointment of a successor Trustee to all
Holders in the manner provided in Section 1.06.  Each notice shall include the
name of the successor Trustee and the address of its Corporate Trust Office.

                 SECTION 6.11.  Acceptance of Appointment by Successor.  Every
successor Trustee appointed hereunder shall execute, acknowledge and deliver to
the Company and to the retiring Trustee an instrument accepting such
appointment, and thereupon the resignation or removal of the retiring Trustee
shall become effective and such successor Trustee, without any further act,
deed or conveyance, shall become vested with all the rights, powers, trusts and
duties of the retiring Trustee; but, on the request of the Company or the
successor Trustee, such retiring Trustee shall, upon payment of its charges,
execute and deliver an instrument transferring to such successor Trustee all
the
<PAGE>   53
                                                                              47




rights, powers and trusts of the retiring Trustee and shall duly assign,
transfer and deliver to such successor Trustee all property and money held by
such retiring Trustee hereunder.  Upon request of any such successor Trustee,
the Company shall execute any and all instruments for more fully and certainly
vesting in and confirming to such successor Trustee all such rights, powers and
trusts.

                 No successor Trustee shall accept its appointment unless at
the time of such acceptance such successor Trustee shall be qualified and
eligible under this Article VI.

                 SECTION 6.12.  Merger, Conversion, Consolidation or Succession
to Business.  Any corporation into which the Trustee may be merged or converted
or with which it may be consolidated, or any corporation resulting from any
merger, conversion or consolidation to which the Trustee shall be a party, or
any corporation succeeding to all or substantially all the corporate trust
business of the Trustee, shall be the successor of the Trustee hereunder;
provided such corporation shall be otherwise qualified and eligible under this
Article VI without the execution or filing of any paper or any further act on
the part of any of the parties hereto.  In case any Securities shall have been
authenticated, but not delivered, by the Trustee then in office, any successor
by merger, conversion or consolidation to such authenticating Trustee may adopt
such authentication and deliver the Securities so authenticated with the same
effect as if such successor Trustee had itself authenticated such Securities.

                 SECTION 6.13.  Preferential Collection of Claims Against
Company.  If and when the Trustee shall be or become a creditor of the Company
(or any other obligor upon the Securities), the Trustee shall be subject to the
provisions of the Trust Indenture Act regarding the collection of claims
against the Company (or any such other obligor).

                 SECTION 6.14.  Appointment of Authenticating Agent.  The
Trustee may appoint an Authenticating Agent or Agents which shall be authorized
to act on behalf of the Trustee to authenticate Securities issued upon original
issue and upon exchange, registration of transfer, partial conversion, partial
redemption, or partial repurchase or pursuant to Section 3.06, and Securities
so authenticated shall be entitled to the benefits of this Indenture and shall
be valid and obligatory for all purposes as if authenticated by the Trustee
hereunder.  Wherever reference is made in this Indenture to the authentication
and delivery of Securities by the Trustee or the Trustee's certificate of
authentication, such reference shall be deemed to include authentication and
delivery on behalf of the Trustee by an Authenticating Agent and a certificate
of authentication executed on behalf of the Trustee by an Authenticating Agent.
Each Authenticating Agent shall be acceptable to the Company and shall at all
times be a corporation organized and doing business under the laws of the
United States, authorized under such laws to act as Authenticating Agent, which
shall have (or, in the case of a corporation included in a bank holding company
system, the related bank holding company shall have) a combined capital and
surplus of not less than U.S.$50,000,000 and be subject to supervision or
examination by Federal or State authority.  If such Authenticating Agent
publishes reports of condition at least annually, pursuant to law or to the
requirements of said supervising or examining authority, then, for the purposes
of this Section, the combined capital and surplus of such Authenticating Agent
or related bank holding company shall be deemed to be its combined capital and
surplus as set forth in its most recent report of condition so published.  If
at any time an Authenticating Agent shall cease to be eligible in accordance
<PAGE>   54
                                                                              48




with the provisions of this Section, such Authenticating Agent shall resign
immediately in the manner and with the effect specified in this Section.

                 Any corporation into which an Authenticating Agent may be
merged or converted or with which it may be consolidated, or any corporation
resulting from any merger, conversion or consolidation to which such
Authenticating Agent shall be a party, or any corporation succeeding to all or
substantially all the corporate agency or corporate trust business of an
Authenticating Agent, shall continue to be an Authenticating Agent; provided
such corporation shall be otherwise eligible under this Section, without the
execution or filing of any paper or any further act on the part of the Trustee
or the Authenticating Agent.

                 An Authenticating Agent may resign at any time by giving
written notice thereof to the Trustee and to the Company.  The Trustee may at
any time terminate the agency of an Authenticating Agent by giving written
notice thereof to such Authenticating Agent and to the Company.  Upon receiving
such a notice of resignation or upon such a termination, or in case at any time
such Authenticating Agent shall cease to be eligible in accordance with the
provisions of this Section 6.14, the Trustee may appoint a successor
Authenticating Agent which shall be acceptable to the Company and shall mail
written notice of such appointment by first-class mail, postage prepaid, to all
Holders as their names and addresses appear in the Security Register.  Any
successor Authenticating Agent upon acceptance of its appointment hereunder
shall become vested with all the rights, powers and duties of its predecessor
hereunder, with like effect as if originally named as an Authenticating Agent.
No successor Authenticating Agent shall be appointed unless eligible under the
provisions of this Section 6.14.

                 The Company agrees to pay to each Authenticating Agent from
time to time compensation for its services under this Section 6.14.

                 If an appointment is made pursuant to this Section, the
Securities may have endorsed thereon, in addition to the Trustee's certificate
of authentication, an alternative certificate of authentication in the
following form:

                 This is one of the Securities described in the
within-mentioned Indenture.


                                                        The Bank of New York
                                                  -----------------------------
                                                             As Trustee

                                                By
                                                  -----------------------------
                                                      As Authenticating Agent

                                                By
                                                  -----------------------------
                                                      Authorized Signatory

                 SECTION 6.15.  Appointment of Co-Trustee.  Subject to the
qualifications set forth in Section 6.09, the Trustee may appoint an additional
institution as a separate trustee or co-trustee. If the Trustee appoints an
additional institution as a separate trustee or co-trustee, each and every
remedy, power, fight, claim, demand, cause of action,
<PAGE>   55
                                                                              49




immunity, estate, duty, obligation, title, interest and lien expressed or
intended by this Indenture to be exercised by, vested in and conveyed by the
Trustee with respect thereto shall be exercisable by, vested in and conveyed to
such separate trustee or co-trustee, but only to the extent necessary to enable
such separate trustee or co-trustee to exercise such powers, rights and
remedies, and every covenant and obligation necessary for the exercise thereby
by such separate trustee or co-trustee shall run to and be enforceable by
either of them.  Should any instrument in writing from the Company be required
by the separate trustee or co-trustee so appointed by the Trustee for more
fully vesting in and confirming to them such properties, rights, powers,
trusts, duties and obligations, any and all such instruments in writing shall,
on request, be executed, acknowledged and delivered by the Company.  If any
separate trustee or co-trustee, or a successor to either, shall become
incapable of acting or not qualified to act, resign or be removed, all the
estate, properties, rights, powers, trusts, duties and obligations of such
separate trustee or co-trustee, so far as permitted by law, shall vest in and
be exercised by the Trustee until the appointment of a successor to such
separate trustee or co-trustee.  The appointment of any separate trustee or
co-trustee shall be subject to written approval of the Company so long as no
Event of Default has occurred and is continuing under this Indenture.


                                  ARTICLE VII

               Holders' Lists and Reports by Trustee and Company

                 SECTION 7.01.  Company To Furnish Trustee Names and Addresses
of Holders.  The Company will furnish or cause to be furnished to the Trustee

                 (a) semi-annually, not more than 15 days after each Regular
     Record Date, a list, in such form as the Trustee may reasonably require,
     of the names and addresses of the Holders as of such Regular Record Date,
     and

                 (b) at such other times as the Trustee may request in writing,
     within 30 days after the receipt by the Company of any such request, a
     list of similar form and content as of a date not more than 15 days prior
     to the time such list is furnished;

excluding from any such list names and addresses received by the Trustee in its
capacity as Security Registrar.

                 SECTION 7.02.  Preservation of Information; Communications to
Holders.  (a)  The Trustee shall preserve, in as current a form as is
reasonably practicable, the names and addresses of Holders contained in the
most recent list furnished to the Trustee as provided in Section 7.01 and the
names and addresses of Holders received by the Trustee in its capacity as
Security Registrar.  The Trustee may destroy any list furnished to it as
provided in Section 7.01 upon receipt of a new list so furnished.

                 (b)  The rights of Holders to communicate with other Holders
with respect to their rights under this Indenture or under the Securities, and
the corresponding rights and duties of the Trustee, shall be as provided by the
Trust Indenture Act.

                 (c)  Every Holder of Securities, by receiving and holding the
same, agrees with the Company and the Trustee that neither the Company nor the
Trustee nor any agent of either of them shall be held accountable by reason of
any disclosure of
<PAGE>   56
                                                                              50




information as to names and addresses of Holders made pursuant to the Trust
Indenture Act.

                 SECTION 7.03.  Reports by Trustee.  (a)  The Trustee shall
transmit to Holders within 60 days after May 15th of each year such reports
concerning the Trustee and its actions under this Indenture as may be required
pursuant to the Trust Indenture Act at the times and in the manner provided
pursuant thereto.

                 (b)  A copy of each such report shall, at the time of such
transmission to Holders, be filed by the Trustee with each stock exchange upon
which the Securities are listed, with the Commission, if applicable, and with
the Company.  The Company will promptly notify the Trustee when the Securities
are listed on any stock exchange and of any delisting thereof.

                 SECTION 7.04.  Reports by Company.  (a)  The Company shall
file with the Trustee and the Commission, if applicable, and transmit to
Holders, such information, documents and other reports, and such summaries
thereof, as may be required pursuant to the Trust Indenture Act at the times
and in the manner provided pursuant to such Act; provided that any such
information, documents or reports required to be filed with the Commission
pursuant to Section 13 or 15(d) of the Exchange Act shall be filed with the
Trustee within 15 days after the same is so required to be filed with the
Commission.  Delivery of such reports, information and documents to the Trustee
is for informational purposes only, and the Trustee's receipt of such shall not
constitute constructive notice of any information contained therein or
determinable from information contained therein, including the Company's
compliance with any of its covenants hereunder (as to which the Trustee is
entitled to rely exclusively on Officers' Certificates).  Notwithstanding
anything to the contrary contained herein, the Trustee shall have no duty to
review such documents for the purpose of determining compliance with this
Indenture.

                 (b)  The Company shall provide the Trustee with at least 30
days' prior notice of any change in location of its principal executive offices
or other principal place of business.


                                  ARTICLE VIII

              Consolidation, Merger, Conveyance, Transfer or Lease

                 SECTION 8.01.  Company May Consolidate, etc., Only on Certain
Terms.  The Company shall not consolidate with or merge into any other Person
or, directly or indirectly, convey, transfer, sell, lease or otherwise dispose
of all or substantially all of its properties and assets to any Person, and the
Company shall not permit any Person to consolidate with or merge into the
Company or convey, transfer, sell, lease or otherwise dispose of all or
substantially all of its properties and assets to the Company, unless:

                 (1) in case the Company shall consolidate with or merge into
     another Person or convey, transfer or lease its properties and assets
     substantially as an entirety to any Person, the Person formed by such
     consolidation or into which the Company is merged or the Person which
     acquires by conveyance or transfer, or which leases, the properties and
     assets of the Company substantially as an entirety (i) shall be a
     corporation, partnership or trust, (ii)  shall be an entity (A) organized
     and
<PAGE>   57
                                                                              51




     validly existing under the laws of the United States of America, any State
     thereof or the District of Columbia or (B) organized and validly existing
     under the laws of a jurisdiction outside of the United States of America,
     with its common stock, or American Depositary Shares representing such
     shares of common stock, traded on a national securities exchange in the
     United States of America or through Nasdaq and an average worldwide total
     market capitalization of its equity securities of at least U.S. $5 billion
     during the ten Trading Days immediately preceding the date of the Change
     in Control, and (iii) shall expressly assume, by an indenture supplemental
     hereto, executed and delivered to the Trustee, in form satisfactory to the
     Trustee, the due and punctual payment of the principal of and premium, if
     any (including the Make-Whole Payment, if any), and interest (including
     Additional Interest) on all the Securities and the performance or
     observance of every covenant of this Indenture on the part of the Company
     to be performed or observed and shall have provided for conversion rights
     in accordance with Article XIII;

                 (2) immediately after giving effect to such transaction, no
     Event of Default, and no event which, after notice or lapse of time or
     both, would become an Event of Default, shall have happened and be
     continuing; and

                 (3) the Company has delivered to the Trustee an Officers'
     Certificate and an Opinion of Counsel, each stating that such
     consolidation, merger, conveyance, transfer or lease and, if a
     supplemental indenture is required in connection with such transaction,
     such supplemental indenture comply with this Article VIII and that all
     conditions precedent herein provided for relating to such transaction have
     been complied with.

                 SECTION 8.02.  Successor Substituted.  Upon any consolidation
of the Company with, or merger of the Company into, any other Person or any
conveyance, transfer or lease of the properties and assets of the Company
substantially as an entirety in accordance with Section 8.01, the successor
Person formed by such consolidation or into which the Company is merged or to
which such conveyance, transfer or lease is made shall succeed to, and be
substituted for, and may exercise every right and power of, the Company under
this Indenture with the same effect as if such successor Person had been named
as the Company herein, and thereafter, except in the case of a lease, the
predecessor Person shall be released from its obligations and covenants under
this Indenture and the Securities.


                                   ARTICLE IX

                            Supplemental Indentures

                 SECTION 9.01.  Supplemental Indentures Without Consent of
Holders.  Without the consent of any Holders, the Company, when authorized by a
Board Resolution, and the Trustee, at any time and from time to time, may enter
into one or more indentures supplemental hereto, in form satisfactory to the
Trustee, for any of the following purposes:

                 (1) to evidence the succession of another Person to the
     Company and the assumption by any such successor of the covenants of the
     Company herein and in the Securities; or
<PAGE>   58
                                                                              52



                 (2) to add to the covenants of the Company for the equal and
     ratable benefit of the Holders, or to surrender any right or power herein
     conferred upon the Company; or

                 (3) to make any change to this Indenture that would provide
     any additional benefit or right to the Holders; provided that any such
     action pursuant to this clause (3) shall not adversely affect the
     interests of the Holders of Securities; or

                 (4) to secure the Company's obligations in respect of the
     Securities; or

                 (5) to make provision with respect to the conversion rights of
     Holders pursuant to the requirements of Article XIII; or

                 (6) to make any changes or modifications to this Indenture
     necessary in connection with the registration of any Transfer Restricted
     Securities under the Securities Act as contemplated by Section 10.11;
     provided that any such action pursuant to this clause (6) shall not
     adversely affect the interests of the Holders of Securities; or

                 (7) to cure any ambiguity, to correct or supplement any
     provision herein which may be inconsistent with any other provision
     herein, to correct or supplement any provision herein which limits,
     qualifies or conflicts with a provision of the Trust Indenture Act which
     is required under such Act to be a part of and govern this Indenture, in
     any case to the extent necessary to qualify this Indenture under the Trust
     Indenture Act, or to make any other provisions with respect to matters or
     questions arising under this Indenture which shall not be inconsistent
     with the provisions of this Indenture; provided that such action pursuant
     to this clause (7) shall not adversely affect the interests or legal
     rights of the Holders in any material respect.

                 SECTION 9.02.  Supplemental Indentures with Consent of
Holders.  With the consent of the Holders of not less than a majority in
principal amount of the Outstanding Securities, by the Act of said Holders
delivered to the Company and the Trustee, the Company, when authorized by a
Board Resolution, and the Trustee may enter into an indenture or indentures
supplemental hereto for the purpose of adding any provisions to or changing in
any manner or eliminating any of the provisions of this Indenture or of
modifying in any manner the rights of the Holders under this Indenture;
provided, however, that no such supplemental indenture shall, without the
consent of the Holder of each Outstanding Security affected thereby,

                 (1) change the Stated Maturity of the principal of, or any
     installment of interest on, any Security, or reduce the principal amount
     thereof or the rate of interest thereon or any premium (including the
     Make-Whole Payment) payable upon the redemption thereof, or change the
     place of payment where, or the coin or currency in which, any Security or
     any premium (including the Make-Whole Payment) or interest thereon is
     payable, or impair the right to institute suit for the enforcement of any
     such payment on or after the Stated Maturity thereof (or, in the case of
     redemption or repurchase, on or after the Redemption Date or Repurchase
     Date, as the case may be), or adversely affect the right to convert any
     Security as provided in Article XIII (except as permitted by Section
     9.01(5)), or modify the provisions of this Indenture with respect to the
     subordination of the Securities in a manner adverse to
<PAGE>   59
                                                                              53




     the Holders, or modify the redemption provisions in a manner adverse to
     the Holders, or modify the provisions relating to the Company's
     requirement to offer to repurchase Notes upon a Change in Control in a
     manner adverse to the Holders, or

                 (2) modify any of the provisions of this Section 9.02, Section
     5.13 or Section 10.08, except to increase any such percentage or to
     provide that certain other provisions of this Indenture cannot be modified
     or waived without the consent of the Holder of each Outstanding Security
     affected thereby, or

                 (3) modify the obligation of the Company to maintain an office
     or agency in the Borough of Manhattan, The City of New York  pursuant to
     Section 10.02, or

                 (4) modify any of the provisions of Section 10.09 or Section
     10.10, or

                 (5) reduce the percentage in principal amount of the
     Outstanding Securities, the consent of whose Holders is required for any
     such supplemental indenture, or the consent of whose Holders is required
     for any waiver (of compliance with certain provisions of this Indenture or
     certain defaults hereunder and their consequences) provided for in this
     Indenture.

                 It shall not be necessary for any Act of Holders under this
Section 9.02 to approve the particular form of any proposed supplemental
indenture, but it shall be sufficient if such Act shall approve the substance
thereof.

                 SECTION 9.03.  Execution of Supplemental Indentures.  In
executing, or accepting the additional trusts created by, any supplemental
indenture permitted by this Article IX or the modifications thereby of the
trusts created by this Indenture, the Trustee shall receive, and (subject to
Section 6.01 and Section 6.03) shall be fully protected in relying upon, an
Opinion of Counsel stating that the execution of such supplemental indenture is
authorized or permitted by this Indenture, complies with its terms and will,
upon the execution and delivery thereof, be valid and binding upon the Company
in accordance with its terms.  The Trustee may, but shall not be obligated to,
enter into any such supplemental indenture which affects the Trustee's own
rights, duties or immunities under this Indenture or otherwise.

                 SECTION 9.04. Effect of Supplemental Indentures. Upon the
execution of any supplemental indenture under this Article, this Indenture
shall be modified in accordance therewith, and such supplemental indenture
shall form a part of this Indenture for all purposes; and every Holder of
Securities theretofore or thereafter authenticated and delivered hereunder
shall be bound thereby.

                 SECTION 9.05. Conformity with Trust Indenture Act.  Every
supplemental indenture executed pursuant to this Article shall conform to the
requirements of the Trust Indenture Act.

                 SECTION 9.06.  Reference in Securities to Supplemental
Indentures.  Securities authenticated and delivered after the execution of any
supplemental indenture pursuant to this Article may, and shall if required by
the Trustee, bear a notation in form approved by the Trustee as to any matter
provided for in such supplemental indenture.  If the Company shall so
determine, new Securities so modified as to conform, in the judgment of the
Trustee and the Company, to any such supplemental indenture may be
<PAGE>   60
                                                                              54




prepared and executed by the Company and authenticated and delivered by the
Trustee in exchange for Outstanding Securities.


                                   ARTICLE X

                                   Covenants

                 SECTION 10.01.  Payment of Principal, Premium and Interest.
The Company will duly and punctually pay the principal of and premium, if any
(including the Make-Whole Payment, if any, upon redemption pursuant to Article
XI), and interest on the Securities in accordance with the terms of the
Securities and this Indenture.

                 SECTION 10.02.  Maintenance of Office or Agency.  The Company
will maintain in the Borough of Manhattan, The City of New York  an office or
agency where Securities may be presented or surrendered for payment, where
Securities may be surrendered for registration of transfer or exchange, where
Securities may be surrendered for conversion and where notices and demands to
or upon the Company in respect of the Securities and this Indenture may be
served.  The Company will give prompt written notice to the Trustee of the
location, and any change in the location, of such office or agency.  If at any
time the Company shall fail to maintain any such required office or agency or
shall fail to furnish the Trustee with the address thereof, such presentations,
surrenders, notices and demands may be made or served at the Corporate Trust
Office of the Trustee or the office or agency of the Trustee in the Borough of
Manhattan, The City of New York.  The Company hereby appoints the Trustee as
its agent to receive all such presentations, surrenders, notices and demands.

                 The Company may also from time to time designate one or more
other offices or agencies (in or outside the Borough of Manhattan, The City of
New York) where the Securities may be presented or surrendered for any or all
such purposes and may from time to time rescind such designations; provided,
however, that no such designation or rescission shall in any manner relieve the
Company of its obligation to maintain an office or agency in the Borough of
Manhattan, The City of New York for such purposes.  The Company will give
prompt written notice to the Trustee of any such designation or rescission and
of any change in the location of any such other office or agency.

                 SECTION 10.03.  Money for Security Payments To Be Held in
Trust.  If the Company shall at any time act as its own Paying Agent, it will,
on or before each due date of the principal of and premium, if any (including
the Make-Whole Payment, if any), or interest (together with any Additional
Interest in respect thereof) on any of the Securities, segregate and hold in
trust for the benefit of the Persons entitled thereto a sum sufficient to pay
the principal and premium, if any (including the Make-Whole Payment, if any),
or interest (together with any Additional Interest in respect thereof) so
becoming due until such sums shall be paid to such Persons or otherwise
disposed of as herein provided and will promptly notify the Trustee of its
action or failure so to act.

                 Whenever the Company shall have one or more Paying Agents, it
will, prior to each due date of the principal of and premium, if any (including
the Make-Whole Payment, if any), or interest (together with any Additional
Interest in respect thereof) on any Securities, deposit with a Paying Agent a
sum sufficient to pay such amount, such
<PAGE>   61
                                                                              55




sum to be held in trust for the benefit of the Persons entitled to such
principal, premium, if any (including the Make-Whole Payment, if any), or
interest, and (unless such Paying Agent is the Trustee) the Company will
promptly notify the Trustee of its action or failure so to act.

                 The Company will cause each Paying Agent other than the
Trustee to execute and deliver to the Trustee an instrument in which such
Paying Agent shall agree with the Trustee, subject to the provisions of this
Section 10.03, that such Paying Agent will:

                 (1) hold all sums held by it for the payment of the principal
     of, premium, if any (including the Make-Whole Payment, if any), or
     interest on Securities in trust for the benefit of the Persons entitled
     thereto until such sums shall be paid to such Persons or otherwise
     disposed of as herein provided;

                 (2) give the Trustee notice of any default by the Company (or
     any other obligor upon the Securities) in the making of any payment of
     principal, premium, if any (including the Make-Whole Payment, if any), or
     interest; and

                 (3) at any time during the continuance of any such default,
     upon the written request of the Trustee, forthwith pay to the Trustee all
     sums so held in trust by such Paying Agent.

                 The Company may at any time, for the purpose of obtaining the
satisfaction and discharge of this Indenture or for any other purpose, pay, or
by Company Order direct any Paying Agent to pay, to the Trustee all sums held
in trust by the Company or such Paying Agent, such sums to be held by the
Trustee upon the same trusts as those upon which such sums were held by the
Company or such Paying Agent; and, upon such payment by any Paying Agent to the
Trustee, such Paying Agent shall be released from all further liability with
respect to such money.

                 Any money deposited with the Trustee or any Paying Agent, or
then held by the Company, in trust for the payment of the principal of and
premium, if any (including the Make-Whole Payment, if any), or interest
(together with any Additional Interest in respect thereof) on any Security and
remaining unclaimed for two years after such principal and premium, if any
(including the Make-Whole Payment, if any), or interest has become due and
payable shall be paid to the Company on Company Request, or (if then held by
the Company) shall be discharged from such trust; and the Holder of such
Security shall thereafter, as an unsecured general creditor, look only to the
Company for payment thereof, and all liability of the Trustee or such Paying
Agent with respect to such trust money, and all liability of the Company as
trustee thereof, shall thereupon cease; provided, however, that the Trustee or
such Paying Agent, before being required to make any such repayment, may at the
expense of the Company cause to be published once, in a newspaper published in
the English language, customarily published on each Business Day and of general
circulation in the Borough of Manhattan, The City of New York, notice that such
money remains unclaimed and that, after a date specified therein, which shall
not be less than 30 days from the date of such publication, any unclaimed
balance of such money then remaining will be repaid to the Company.

                 SECTION 10.04.  Statement by Officers as to Default.  The
Company shall deliver to the Trustee, within 120 days after the end of each
fiscal year of the
<PAGE>   62
                                                                              56




Company ending after the date hereof, an Officers' Certificate, stating whether
or not to the best knowledge of the signers thereof the Company is in default
in the performance and observance of any of the terms, provisions and
conditions of this Indenture (without regard to any period of grace or
requirement of notice provided hereunder) and, if the Company shall be in
default, specifying all such defaults and the nature and status thereof of
which they may have knowledge.

                 SECTION 10.05.  Existence.  Subject to Article VIII, the
Company shall do or cause to be done all things necessary to preserve and keep
in full force and effect its existence, rights (charter and statutory) and
franchises; provided, however, that the Company shall not be required to
preserve any such right or franchise if the Board of Directors shall determine
that the preservation thereof is no longer desirable in the conduct of the
business of the Company and that the loss thereof is not disadvantageous in any
material respect to the Holders.

                 SECTION 10.06.  Maintenance of Properties.  The Company shall
cause all properties used or useful in the conduct of its business or the
business of any Subsidiary to be maintained and kept in good condition, repair
and working order and supplied with all necessary equipment and shall cause to
be made all necessary repairs, renewals, replacements, betterments and
improvements thereof, all as in the judgment of the Company may be necessary so
that the business carried on in connection therewith may be properly and
advantageously conducted at all times; provided, however, that nothing in this
Section 10.06 shall prevent the Company from discontinuing the operation or
maintenance of any of such properties, or disposing of any of them, if such
discontinuance or disposition is, in the judgment of the Company, desirable in
the conduct of its business or the business of any Subsidiary and not
disadvantageous in any material respect to the Holders.

                 SECTION 10.07.  Payment of Taxes and Other Claims.  The
Company shall pay or discharge or cause to be paid or discharged, before the
same shall become delinquent, (1) all taxes, assessments and governmental
charges levied or imposed upon the Company or any Subsidiary or upon the
income, profits or property of the Company or any Subsidiary, and (2) all
lawful claims for labor, materials and supplies which, if unpaid, might by law
become a lien upon the property of the Company or any Subsidiary; provided,
however, that the Company shall not be required to pay or discharge or cause to
be paid or discharged any such tax, assessment, charge or claim whose amount,
applicability or validity is being contested in good faith by appropriate
proceedings.

                 SECTION 10.08.  Waiver of Certain Covenants.  The Company may
omit in any particular instance to comply with any covenant or condition set
forth in Sections 10.05 to 10.07, inclusive, if before the time for such
compliance the Holders of at least a majority in principal amount of the
Outstanding Securities shall, by Act of such Holders, either waive such
compliance in such instance or generally waive compliance with such covenant or
condition, but no such waiver shall extend to or affect such covenant or
condition except to the extent so expressly waived, and, until such waiver
shall become effective, the obligations of the Company and the duties of the
Trustee in respect of any such covenant or condition shall remain in full force
and effect.

                 SECTION 10.09.  Delivery of Certain Information.  At any time
when the Company is not subject to Section 13 or 15(d) of the Exchange Act,
upon the request of a Holder or the holder of shares of Common Stock issued
upon conversion thereof, the
<PAGE>   63
                                                                              57




Company shall promptly furnish or cause to be furnished Rule 144A Information
(as defined below) to such Holder or such holder of shares of Common Stock
issued upon conversion of Securities, or to a prospective purchaser of any such
security designated by any such Holder or holder, as the case may be, to the
extent required to permit compliance by such Holder or holder with Rule 144A
under the Securities Act in connection with the resale of any such security.
"Rule 144A Information" shall be such information as is specified pursuant to
Rule 144A(d)(4) under the Securities Act.

                 SECTION 10.10.  Resale of Certain Securities; Reporting
Issuer.  During the period beginning on the last date of original issuance of
the Securities and ending on the date that is two years from such date, the
Company will not, and will use its best efforts not to permit any of its
"affiliates" (as defined under Rule 144 under the Securities Act or any
successor provision thereto) to, resell (x) any Securities which constitute
"restricted securities" under Rule 144 or (y) any securities into which the
Securities have been converted under this Indenture which constitute
"restricted securities" under Rule 144, that in either case have been
reacquired by any of them.  The Trustee shall have no responsibility in respect
of the Company's performance of its agreement in the preceding sentence.

                 SECTION 10.11.  Registration Rights.  (a)  The Company agrees
that the Holders (and any Person that has a beneficial interest in a Security)
from time to time of Transfer Restricted Securities are entitled to the
benefits of a Registration Rights Agreement, dated as of December 14, 1999 (the
"Registration Rights Agreement"), executed by the Company.  Pursuant to the
Registration Rights Agreement, the Company has agreed for the benefit of the
Holders from time to time of Transfer Restricted Securities, at the Company's
expense, (i) to file within 60 days after the first date of original issuance
of the Securities, a shelf registration statement (the "Shelf Registration
Statement") with the Commission with respect to resales of the Transfer
Restricted Securities, (ii) to use its best efforts to cause such Shelf
Registration Statement to be declared effective by the Commission not later
than 120 days after the first date of original issuance of the Securities, and
(iii) to use its best efforts to maintain such Shelf Registration Statement
continuously effective under the Securities Act subject to and in accordance
with the terms of the Registration Rights Agreement.

                 Additional interest (the "Additional Interest") with respect
to the Securities shall be assessed as follows if any of the following events
occur (each such event in clauses (i) through (iii) below being herein called a
"Registration Default"):

              (i)   if on or prior to the 60th day after the first date of
     original issuance of the Securities the Shelf Registration Statement has
     not been filed with the Commission;

             (ii)   if on or prior to the 120th day after the first date of
     original issuance of the Securities the Shelf Registration Statement has
     not been declared effective by the Commission; or

            (iii)   if after the Shelf Registration Statement is declared
     effective (A) the Shelf Registration Statement thereafter ceases to be
     effective; or (B) the Shelf Registration Statement or the related
     prospectus ceases to be usable (in each case except as permitted in the
     Registration Rights Agreement) in connection with resales of Transfer
     Restricted Securities in accordance with and during the periods specified
<PAGE>   64
                                                                              58




     herein because either (1) any event occurs as a result of which the
     related prospectus forming part of such Shelf Registration Statement would
     include any untrue statement of a material fact or omit to state any
     material fact necessary to make the statements therein in the light of the
     circumstances under which they were made not misleading, or (2) it shall
     be necessary to amend such Shelf Registration Statement or supplement the
     related prospectus, to comply with the Securities Act or the Exchange Act
     or the respective rules thereunder.

                 Additional Interest shall accrue on the Securities over and
above the interest set forth in the title of the Securities from and including
the date on which any such Registration Default shall occur, to but excluding
the date on which all such Registration Defaults have been cured, at a rate of
0.50% per annum.

                 (b)  Any amounts of Additional Interest due pursuant to clause
(a)(i), (a)(ii) or (a)(iii) of this Section 10.11 shall be payable in cash on
the regular Interest Payment Dates.  The amount of Additional Interest shall be
determined by multiplying the applicable Additional Interest rate by the
principal amount of the Securities, multiplied by a fraction, the numerator of
which is the number of days such Additional Interest rate was applicable during
such period (determined on the basis of a 360-day year comprised of twelve
30-day months), and the denominator of which is 360.

                 Whenever in this Indenture there is mentioned, in any context,
the payment of the principal of, premium, if any, or interest on, or in respect
of, any Security, such mention shall be deemed to include mention of the
payment of Additional Interest provided for in this Section to the extent that,
in such context, Additional Interest are, were or would be payable in respect
thereof pursuant to the provisions of this Section 10.11 and express mention of
the payment of Additional Interest (if applicable) in any provisions hereof
shall not be construed as excluding Additional Interest in those provisions
hereof where such express mention is not made.


                                   ARTICLE XI

                            Redemption of Securities

                 SECTION 11.01.  Right of Provisional Redemption.  The
Securities may be redeemed by the Company (a "Provisional Redemption"), in
whole or in part, at any time prior to December 20, 2002, upon notice as set
forth in Section 11.06, at a redemption price equal to $1,000 per Security to
be redeemed plus accrued and unpaid interest, if any (including Additional
Interest, if any), to the date of redemption (the "Provisional Redemption
Date") if (i) the closing price of the Common Stock shall have exceeded 150% of
the conversion price then in effect for at least 20 Trading Days in any
consecutive 30-Trading Day period ending on the Trading Day prior to the date
of mailing of the notice of redemption pursuant to Section 11.06 (the
"Redemption Notice Date") and (ii) the Shelf Registration Statement is
effective and available for use and is expected to remain effective and
available for use for the 30 days immediately following the Provisional
Redemption Date.  Upon any such Provisional Redemption, the Company shall make
an additional payment in cash (the "Make-Whole Payment") with respect to the
Securities called for redemption to Holders on the Redemption Notice Date in an
amount equal to $150.00 per $1,000 Security, less the amount of any interest
actually paid on such Security prior to the Redemption Notice Date.  The
Company shall make the
<PAGE>   65
                                                                              59




Make-Whole Payment on all Securities called for Provisional Redemption,
including any Securities converted into Common Stock pursuant to the terms
hereof after the Redemption Notice Date and prior to the Provisional Redemption
Date.

                 SECTION 11.02.  Right of Optional Redemption.  The Securities
may be redeemed at the election of the Company (an "Optional Redemption"), as a
whole or from time to time in part, at any time on or after December 20, 2002
through December 14, 2003 at 102.50% of the principal amount, and thereafter,
at the following Redemption Prices (expressed as percentages of the principal
amount), if redeemed during the 12-month period beginning on December 15 of the
years indicated,

<TABLE>
<CAPTION>
                                                 Redemption
      Year                                         Price
      ----                                    -----------------
 <S>                                         <C>
      2003 .............................          101.67%
      2004 .............................          100.83%
      2005 .............................          100.00%
</TABLE>


and thereafter at a Redemption Price equal to 100% of the principal amount,
together in the case of any such redemption with accrued interest to (but not
including) the Redemption Date, but interest installments whose Stated Maturity
is on or prior to such Redemption Date will be payable to the Holders of such
Securities, or one or more Predecessor Securities, of record at the close of
business on the relevant Record Dates referred to on the face hereof, all as
provided in this Indenture.

                 SECTION 11.03.  Applicability of Article.  Redemption of
Securities at the election of the Company or otherwise, as permitted or
required by any provision of this Indenture, shall be made in accordance with
such provision and this Article XI.

                 SECTION 11.04.  Election to Redeem; Notice to Trustee.  The
election of the Company to redeem any Securities pursuant to Section 11.01 or
11.02 shall be evidenced by a Board Resolution.  In case of any redemption at
the election of the Company, the Company shall, at least 45 days prior to the
Redemption Date fixed by the Company (unless a shorter notice shall be
satisfactory to the Trustee), notify the Trustee of such Redemption Date and of
the principal amount of Securities to be redeemed.

                 SECTION 11.05.  Selection by Trustee of Securities to Be
Redeemed.  If less than all the Securities are to be redeemed, the particular
Securities to be redeemed shall be selected not less than 20 days or more than
60 days prior to the Redemption Date by the Trustee, from the Outstanding
Securities not previously called for redemption, by lot or by such method as
the Trustee shall deem fair and appropriate in the circumstances and which may
provide for the selection for redemption of portions (equal to U.S.$1,000 or
any integral multiple thereof) of the principal amount of Securities of a
denomination larger than U.S.$1,000.

                 If any Security selected for partial redemption is converted
in part before termination of the conversion right with respect to the portion
of the Security so selected, the converted portion of such Security shall be
deemed (so far as may be) to be the portion selected for redemption.
Securities which have been converted during a selection
<PAGE>   66
                                                                              60




of Securities to be redeemed shall be treated by the Trustee as Outstanding for
the purpose of such selection.

                 The Trustee shall promptly notify the Company and each
Security Registrar in writing of the Securities selected for redemption and, in
the case of any Securities selected for partial redemption, the principal
amount thereof to be redeemed.

                 For all purposes of this Indenture, unless the context
otherwise requires, all provisions relating to the redemption of Securities
shall relate, in the case of any Securities redeemed or to be redeemed only in
part, to the portion of the principal amount of such Securities which has been
or is to be redeemed.

                 SECTION 11.06.  Notice of Redemption.  Notice of redemption
shall be given by first-class mail, postage prepaid, mailed not less than 20
nor more than 60 days prior to the Redemption Date, to each Holder of
Securities to be redeemed, at his address appearing in the Security Register.

                 All notices of redemption shall describe the Securities,
including CUSIP number, and state:

                 (1)  the Redemption Date;

                 (2)  the Redemption Price;

                 (3)  if less than all the Outstanding Securities are to be
     redeemed, the identification (and, in the case of partial redemption of
     any Securities, the principal amounts) of the particular Securities to be
     redeemed;

                 (4)  whether such redemption is a Provisional Redemption or an
     Optional Redemption;

                 (5)  that on the Redemption Date the Redemption Price shall
     become due and payable upon each such Security to be redeemed and that
     interest thereon shall cease to accrue on and after said date;

                 (6)  the conversion price, the date on which the right to
     convert the Securities to be redeemed will terminate and the place or
     places where such Securities may be surrendered for conversion;

                 (7)  the place or places where such Securities are to be
     surrendered for payment of the Redemption Price; and

                 (8)  if such a redemption is a Provisional Redemption, the
     amount of the Make-Whole Payment.

                 Notice of redemption of Securities to be redeemed at the
election of the Company shall be given by the Company or, at the Company's
request, by the Trustee in the name and at the expense of the Company, and
shall be irrevocable.

                 SECTION 11.07.  Deposit of Redemption Price.  On or prior to
any Redemption Date, the Company shall deposit with the Trustee or with a
Paying Agent (or,
<PAGE>   67
                                                                              61




if the Company is acting as its own Paying Agent, segregate and hold in trust
as provided in Section 10.03) (i) an amount of money sufficient to pay the
Redemption Price of, and (except if the Redemption Date shall be an Interest
Payment Date) accrued interest on, all the Securities which are to be redeemed
on that date other than any Securities called for redemption on that date which
have been converted prior to the date of such deposit and (ii) with respect to
Securities called for Provisional Redemption pursuant to Section 11.01, an
amount of money sufficient to pay the Make-Whole Payment for all the Securities
(or portions thereof) called for redemption (including those surrendered for
conversion into Common Stock after the Redemption Notice Date and prior to the
Provisional Redemption Date); provided that if such payment is made on the
Redemption Date, it must be received by the Trustee or Paying Agent, as the
case may be, by 10:00 a.m. New York City time on such date.

                 If any Security called for redemption is converted, any money
deposited with the Trustee or with any Paying Agent or so segregated and held
in trust for the redemption of such Security shall (subject to any right of the
Holder of such Security or any Predecessor Security to receive interest as
provided in the last paragraph of Section 3.07) be paid to the Company as soon
as practicable upon Company Request or, if then held by the Company, shall be
released from such trust; provided that, with respect to a Provisional
Redemption, any money so deposited for payment of the Make-Whole Payment shall
remain segregated and held in trust for payment of the Make-Whole Payment which
shall be made on all Securities called for Provisional Redemption, including
Securities converted into Common Stock after the Redemption Notice Date and
prior to the Provisional Redemption Date.

                 SECTION 11.08.  Securities Payable on Redemption Date.  Notice
of redemption having been given as aforesaid, the Securities so to be redeemed
shall, on the Redemption Date, become due and payable at the Redemption Price
therein specified, and, with respect to Securities called for Provisional
Redemption, the Make-Whole Payment, and from and after such date (unless the
Company shall default in the payment of the Redemption Price and accrued
interest or the Make-Whole Payment, if any) such Securities shall cease to bear
or accrue any interest.  Upon surrender of any such Security for redemption in
accordance with said notice, such Security shall be paid by the Company at the
Redemption Price, together with accrued interest to (but not including) the
Redemption Date and, with respect to Securities called for Provisional
Redemption (including Securities converted into Common Stock pursuant to the
terms hereof after the Redemption Notice Date and prior to the Provisional
Redemption Date), the Make-Whole Payment; provided, however, that installments
of interest whose Stated Maturity is on or prior to the Redemption Date shall
be payable to the Holders of such Securities, or one or more Predecessor
Securities, registered as such at the close of business on the relevant Record
Dates according to their terms and the provisions of Section 3.07; and provided
further that, with respect to a Provisional Redemption, the holder of any
Securities converted into Common Stock pursuant to the terms of this Indenture
after the Redemption Notice Date and prior to the Provisional Redemption Date
shall have the right to the Make-Whole Payment, if any, with respect to such
Securities regardless of the conversion of such Securities.

                 If the Company shall fail to deposit the Redemption Price (and
Make-Whole Payment, if any) with the Trustee and any Security called for
redemption shall not be so paid upon surrender thereof for redemption, the
principal and premium, if any
<PAGE>   68
                                                                              62




(including the Make-Whole Payment, if any), shall, until paid, bear and accrue
interest from the Redemption Date at the rate borne by the Security.

                 SECTION 11.09.  Securities Redeemed in Part.  Any Security
which is to be redeemed only in part shall be surrendered at an office or
agency of the Company designated for that purpose pursuant to Section 10.02
(with, if the Company or the Trustee so requires, due endorsement by, or a
written instrument of transfer in form satisfactory to the Company and the
Trustee duly executed by, the Holder thereof or his attorney-in-fact duly
authorized in writing), and the Company shall execute, and the Trustee shall
authenticate and deliver to the Holder of such Security without service charge,
a new Security or Securities, of any authorized denomination as requested by
such Holder, in aggregate principal amount equal to and in exchange for the
unredeemed portion of the principal amount of the Security so surrendered.

                 SECTION 11.10.  Conversion Arrangement on Call for Redemption.
In connection with any redemption of Securities, the Company may arrange for
the purchase and conversion of any Securities by an agreement with one or more
investment bankers or other purchasers to purchase such Securities by paying to
the Trustee in trust for the Holders, on or before the Redemption Date, an
amount not less than the applicable Redemption Price of such Securities,
together with interest accrued to the Redemption Date, and, in connection with
a Provisional Redemption, the Make-Whole Payment.  Notwithstanding anything to
the contrary contained in this Article XI, the obligation of the Company to pay
the Redemption Price of such Securities, together with interest accrued to, but
excluding, the Redemption Date and, in connection with a Provisional
Redemption, the Make-Whole Payment, shall be deemed to be satisfied and
discharged to the extent such amount is so paid by such purchasers.  If such an
agreement is entered into, a copy of which shall be filed with the Trustee
prior to the Redemption Date, any Securities not duly surrendered for
conversion by the holders thereof may, at the option of the Company, be deemed,
to the fullest extent permitted by law, acquired by such purchasers from such
holders and (notwithstanding anything to the contrary contained in Article
XIII) surrendered by such purchasers for conversion, all as of immediately
prior to the close of business on the Redemption Date (and the right to convert
any such Securities shall be deemed to have been extended through such time),
subject to payment of the above amount as aforesaid (including the Make-Whole
Payment, if any, with respect to all Securities called for Provisional
Redemption).  At the direction of the Company, the Trustee shall hold and
dispose of any such amount paid to it in the same manner as it would monies
deposited with it by the Company for the redemption of Securities.  Without the
Trustee's prior written consent, no arrangement between the Company and such
purchasers for the purchase and conversion of any Securities shall increase or
otherwise affect any of the powers, duties, responsibilities or obligations of
the Trustee as set forth in this Indenture, and the Company agrees to indemnify
the Trustee from, and hold it harmless against, any loss, liability or expense
arising out of or in connection with any such arrangement for the purchase and
conversion of any Securities between the Company and such purchasers to which
the Trustee has not consented in writing, including the costs and expenses
incurred by the Trustee in the defense of any claim or liability arising out of
or in connection with the exercise or performance of any of its powers, duties,
responsibilities or obligations under this Indenture.  Nothing in the preceding
sentence shall be deemed to limit the rights and protections afforded to the
Trustee in Article VI hereof, including, but not limited to, the right to
indemnification pursuant to Section 6.07.
<PAGE>   69
                                                                              63




                                  ARTICLE XII

                          Subordination of Securities

                 SECTION 12.01.  Securities Subordinate to Senior Indebtedness.
The Company covenants and agrees, and each Holder of a Security, by his
acceptance thereof, likewise covenants and agrees, that, to the extent and in
the manner hereinafter set forth in this Article XII, the indebtedness
represented by the Securities and the payment of the principal of and premium,
if any (including the Make-Whole Payment, if any), and interest on each and all
of the Securities and all obligations of the Company under this Indenture are
hereby expressly made subordinate and subject in right of payment to the prior
payment in full of all Senior Indebtedness.

                 SECTION 12.02.  Payment over of Proceeds Upon Dissolution,
Etc.  In the event of (a) any insolvency or bankruptcy case or proceeding, or
any receivership, liquidation, reorganization or other similar case or
proceeding in connection therewith, relative to the Company or to its
creditors, as such, or to its assets, or (b) any liquidation, dissolution or
other winding-up of the Company, whether voluntary or involuntary and whether
or not involving insolvency or bankruptcy, or (c) any assignment for the
benefit of creditors or any other marshalling of assets and liabilities of the
Company, then and in any such event the holders of Senior Indebtedness shall be
entitled to receive payment in full of all amounts due or to become due on or
in respect of all Senior Indebtedness, or provision shall be made for such
payment in cash or cash equivalents or otherwise in a manner satisfactory to
the holders of Senior Indebtedness, before the Holders of the Securities are
entitled to receive any payment on account of principal of or premium, if any
(including the Make-Whole Payment, if any), or interest on the Securities, and
to that end the holders of Senior Indebtedness shall be entitled to receive,
for application to the payment thereof, any payment or distribution of any kind
or character, whether in cash, property or securities, which may be payable or
deliverable in respect of the Securities in any such case, proceeding,
dissolution, liquidation or other winding-up or event.

                 In the event that, notwithstanding the foregoing provisions of
this Section 12.02, the Trustee or the Holder of any Security shall have
received any payment or distribution of assets of the Company prohibited by the
foregoing paragraph of any kind or character, whether in cash, property or
securities, before all Senior Indebtedness is paid in full or payment thereof
provided for, and if such fact shall, at or prior to the time of such payment
or distribution, have been made actually known to a Responsible Officer of the
Trustee or, as the case may be, such Holder, then and in such event such
payment or distribution shall be paid over or delivered forthwith to the
trustee in bankruptcy, receiver, liquidating trustee, custodian, assignee,
agent or other Person making payment or distribution of assets of the Company
for application to the payment of all Senior Indebtedness remaining unpaid, to
the extent necessary to pay all Senior Indebtedness in full, after giving
effect to any concurrent payment or distribution to or for the holders of
Senior Indebtedness.

                 For purposes of this Article XII only, the words "cash,
property or securities" shall not be deemed to include shares of capital stock
of the Company as reorganized or readjusted, or securities of the Company or
any other corporation provided for by a plan of reorganization or readjustment
which in either case are subordinated in right of payment to all Senior
Indebtedness which may at the time be outstanding to substantially the same
extent as, or to a greater extent than, the Securities are so
<PAGE>   70
                                                                              64




subordinated as provided in this Article XII.  The consolidation of the Company
with, or the merger of the Company into, another Person or the liquidation or
dissolution of the Company following the conveyance or transfer of its
properties and assets substantially as an entirety to another Person upon the
terms and conditions set forth in Article VIII shall not be deemed a
dissolution, winding-up, liquidation, reorganization, assignment for the
benefit of creditors or marshalling of assets and liabilities of the Company
for the purposes of this Section 12.02 if the Person formed by such
consolidation or into which the Company is merged or which acquires by
conveyance or transfer such properties and assets substantially as an entirety,
as the case may be, shall, as a part of such consolidation, merger, conveyance
or transfer, comply with the conditions set forth in Article VIII.

                 SECTION 12.03.  No Payment When Senior Indebtedness in
Default.  (a)  In the event and during the continuation of any default in the
payment of principal of or premium, if any (including the Make-Whole Payment,
if any), or interest on any Senior Indebtedness beyond any applicable grace
period with respect thereto (unless and until such payment default shall have
been cured or waived in writing by the holders of such Senior Indebtedness), or
(b) in the event any judicial proceeding shall be pending with respect to any
such default, then no payment shall be made by the Company on account of
principal of or premium, if any (including the Make-Whole Payment, if any), or
interest on the Securities or on account of the purchase or other acquisition
of Securities (including pursuant to Articles XI and XIII).

                 In the event that, notwithstanding the foregoing, the Company
shall make any payment to the Trustee or the Holder of any Security prohibited
by the foregoing provisions of this Section 12.03, and if such fact shall, at
or prior to the time of such payment, have been made actually known to a
Responsible Officer of the Trustee or, as the case may be, such Holder, then
and in such event such payment shall be paid over and delivered forthwith to
the Company.

                 The provisions of this Section 12.03 shall not apply to any
payment with respect to which Section 12.02 would be applicable.

                 SECTION 12.04.  Payment Permitted If No Default.  Nothing
contained in this Article XII or elsewhere in this Indenture or in any of the
Securities shall prevent (a) the Company, at any time except during the
pendency of any case, proceeding, dissolution, liquidation or other winding-up,
assignment for the benefit of creditors or other marshalling of assets and
liabilities of the Company referred to in Section 12.02 or under the conditions
described in Section 12.03, from making payments at any time of principal of
and premium, if any (including the Make-Whole Payment, if any), or interest on
the Securities, or (b) the application by the Trustee of any money deposited
with it hereunder to the payment of or on account of the principal of and
premium, if any (including the Make-Whole Payment, if any), or interest on the
Securities or the retention of such payment by the Holders, if, at the time of
such application by the Trustee, a Responsible Officer of the Trustee did not
have actual knowledge that such payment would have been prohibited by the
provisions of this Article XII.

                 SECTION 12.05.  Subrogation to Rights of Holders of Senior
Indebtedness.  Subject to the payment in full of all Senior Indebtedness, and
until the Securities are paid in full, the Holders of the Securities shall be
subrogated (equally and ratably with the holders of all indebtedness of the
Company which by its express terms is
<PAGE>   71
                                                                              65




subordinated to indebtedness of the Company to substantially the same extent as
the Securities are subordinated and is entitled to like rights of subrogation)
to the rights of the holders of such Senior Indebtedness to receive payments
and distributions of cash, property and securities applicable to the Senior
Indebtedness to the extent that payments and distributions otherwise payable to
Holders of Securities have been applied to the payment of Senior Indebtedness
as provided by this Article XII.  For purposes of such subrogation, no payments
or distributions to the holders of the Senior Indebtedness of any cash,
property or securities to which the Holders of the Securities or the Trustee
would be entitled, except for the provisions of this Article XII, and no
payments over pursuant to the provisions of this Article XII to the holders of
Senior Indebtedness by Holders of the Securities or the Trustee, shall, as
among the Company, its creditors other than holders of Senior Indebtedness and
the Holders of the Securities, be deemed to be a payment or distribution by the
Company to or on account of the Senior Indebtedness.

                 SECTION 12.06.  Provisions Solely To Define Relative Rights.
The provisions of this Article XII are and are intended solely for the purpose
of defining the relative rights of the Holders of the Securities on the one
hand and the holders of Senior Indebtedness on the other hand.  Nothing
contained in this Article XII or elsewhere in this Indenture or in the
Securities is intended to or shall

                 (a) impair, as among the Company, its creditors other than
     holders of Senior Indebtedness and the Holders of the Securities, the
     obligation of the Company, which is absolute and unconditional (and which,
     subject to the rights under this Article XII of the holders of Senior
     Indebtedness, is intended to rank equally with all other general
     obligations of the Company), to pay to the Holders of the Securities the
     principal of and premium, if any (including the Make-Whole Payment, if
     any), and interest on the Securities as and when the same shall become due
     and payable in accordance with their terms; or

                 (b) affect the relative rights against the Company of the
     Holders of the Securities and creditors of the Company other than the
     holders of Senior Indebtedness; or

                 (c) prevent the Trustee or the Holder of any Security from
     exercising all remedies otherwise permitted by applicable law upon default
     under this Indenture, subject to the rights, if any, under this Article
     XII of the holders of Senior Indebtedness to receive cash, property and
     securities otherwise payable or deliverable to the Trustee or such Holder.

                 SECTION 12.07.  Trustee to Effectuate Subordination.  Each
Holder of a Security by his acceptance thereof authorizes and directs the
Trustee on his behalf to take such action as may be necessary or appropriate to
effectuate the subordination provided in this Article XII and appoints the
Trustee his attorney-in-fact for any and all such purposes.

                 SECTION 12.08.  No Waiver of Subordination Provisions.  No
right of any present or future holder of any Senior Indebtedness to enforce
subordination as herein provided shall at any time in any way be prejudiced or
impaired by any act or failure to act on the part of the Company or by any act
or failure to act, in good faith, by any such holder, or by any non-compliance
by the Company with the terms, provisions and
<PAGE>   72
                                                                              66




covenants of this Indenture, regardless of any knowledge thereof any such
holder may have or be otherwise charged with.

                 Without in any way limiting the generality of the foregoing
paragraph, the holders of Senior Indebtedness may, at any time and from time to
time, without the consent of or notice to the Trustee or the Holders of the
Securities, without incurring responsibility to the Holders of the Securities
and without impairing or releasing the subordination provided in this Article
XII or the obligations hereunder of the Holders of the Securities to the
holders of Senior Indebtedness, do any one or more of the following:

                 (i) change the manner, place or terms of payment or extend the
     time of payment of, or renew or alter, Senior Indebtedness, or otherwise
     amend or supplement in any manner Senior Indebtedness or any instrument
     evidencing the same or any agreement under which Senior Indebtedness is
     outstanding;

                 (ii) sell, exchange, release or otherwise deal with any
     property pledged, mortgaged or otherwise securing Senior Indebtedness;

                 (iii) release any Person liable in any manner for the
     collection of Senior Indebtedness;

                 (iv) exercise or refrain from exercising any rights against
     the Company and any other Person;

                 (v) apply any and all sums received from time to time to the
     Senior Indebtedness.

                 SECTION 12.09.  Notice to Trustee.  The Company shall give
prompt written notice to the Trustee of any fact known to the Company which
would prohibit the making of any payment to or by the Trustee in respect of the
Securities.  Notwithstanding the provisions of this Article XII or any other
provision of this Indenture, the Trustee shall not be charged with knowledge of
the existence of any facts which would prohibit the making of any payment to or
by the Trustee in respect of the Securities, unless and until the Trustee shall
have received written notice thereof from the Company or a holder of Senior
Indebtedness or from any trustee therefor; and, prior to the receipt of any
such written notice, the Trustee, subject to the provisions of Section 6.01,
shall be entitled in all respects to assume that no such facts exist; provided,
however, that if the Trustee shall not have received the notice provided for in
this Section 12.09 at least two Business Days prior to the date upon which by
the terms hereof any money may become payable for any purpose (including,
without limitation, the payment of the principal of and premium, if any
(including the Make-Whole Payment, if any), or interest on any Security), then,
anything herein contained to the contrary notwithstanding, the Trustee shall
have full power and authority to receive such money and to apply the same to
the purpose for which such money was received and shall not be affected by any
notice to the contrary which may be received by it within two Business Days
prior to such date.

                 Subject to the provisions of Section 6.01, the Trustee shall
be entitled to rely on the delivery to it of a written notice by a Person
representing himself to be a holder of Senior Indebtedness (or a trustee
therefor) to establish that such notice has been given by a holder of Senior
Indebtedness (or a trustee therefor).  In the event that the Trustee determines
in good faith that further evidence is required with respect to the right
<PAGE>   73
                                                                              67




of any Person as a holder of Senior Indebtedness to participate in any payment
or distribution pursuant to this Article XII, the Trustee may request such
Person to furnish evidence to the reasonable satisfaction of the Trustee as to
the amount of Senior Indebtedness held by such Person, the extent to which such
Person is entitled to participate in such payment or distribution and any other
facts pertinent to the rights of such Person under this Article XII, and if
such evidence is not furnished, the Trustee may defer any payment to such
Person pending judicial determination as to the right of such Person to receive
such payment.

                 SECTION 12.10.  Reliance on Judicial Order or Certificate of
Liquidating Agent.  Upon any payment or distribution of assets of the Company
referred to in this Article XII, the Trustee, subject to the provisions of
Section 6.01, and the Holders of the Securities shall be entitled to rely upon
any order or decree entered by any court of competent jurisdiction in which
such insolvency, bankruptcy, receivership, liquidation, reorganization,
dissolution, winding up or similar case or proceeding is pending, or a
certificate of the trustee in bankruptcy, receiver, liquidating trustee,
custodian, assignee for the benefit of creditors, agent or other Person making
such payment or distribution, delivered to the Trustee or to the Holders of
Securities, for the purpose of ascertaining the Persons entitled to participate
in such payment or distribution, the holders of the Senior Indebtedness and
other indebtedness of the Company, the amount thereof or payable thereon, the
amount or amounts paid or distributed thereon and all other facts pertinent
thereto or to this Article XII.

                 SECTION 12.11.  Trustee Not Fiduciary for Holders of Senior
Indebtedness.  The Trustee shall not be deemed to owe any fiduciary duty to the
holders of Senior Indebtedness and shall not be liable to any such holders if
it shall in good faith mistakenly pay over or distribute to Holders of
Securities or to the Company or to any other Person cash, property or
securities to which any holders of Senior Indebtedness shall be entitled by
virtue of this Article XII or otherwise.

                 SECTION 12.12.  Rights of Trustee as Holder of Senior
Indebtedness; Preservation of Trustee's Rights.  The Trustee in its individual
capacity shall be entitled to all the rights set forth in this Article XII with
respect to any Senior Indebtedness which may at any time be held by it, to the
same extent as any other holder of Senior Indebtedness, and nothing in this
Indenture shall deprive the Trustee of any of its rights as such holder.

                 Nothing in this Article XII shall apply to claims of, or
payments to, the Trustee under or pursuant to Section 6.07.

                 SECTION 12.13.  Article Applicable to Paying Agents.  In case
at any time any Paying Agent other than the Trustee shall have been appointed
by the Company and be then acting hereunder, the term "Trustee" as used in this
Article XII shall in such case (unless the context otherwise requires) be
construed as extending to and including such Paying Agent within its meaning as
fully for all intents and purposes as if such Paying Agent were named in this
Article XII in addition to or in place of the Trustee; provided, however, that
Section 12.12 shall not apply to the Company or any Affiliate of the Company if
it or such Affiliate acts as Paying Agent.

                 SECTION 12.14.  Certain Conversions Deemed Payment.  For the
purposes of this Article XII only, (1) the issuance and delivery of junior
securities upon
<PAGE>   74
                                                                              68




conversion of Securities in accordance with Article XIII shall not be deemed to
constitute a payment or distribution on account of the principal of or premium
or interest on Securities or on account of the purchase or other acquisition of
Securities, and (2) the payment, issuance or delivery of cash, property or
securities (other than junior securities) upon conversion of a Security shall
be deemed to constitute payment on account of the principal of such Security.
For the purposes of this Section 12.14, the term "junior securities" means (a)
shares of any stock of any class of the Company and (b) securities of the
Company which are subordinated in right of payment to the prior payment in full
of all Senior Indebtedness which may be outstanding at the time of issuance or
delivery of such securities to substantially the same extent as, or to a
greater extent than, the Securities are so subordinated as provided in this
Article XII.  Nothing contained in this Article XII or elsewhere in this
Indenture or in the Securities is intended to or shall impair, as among the
Company, its creditors other than holders of Senior Indebtedness and the
Holders of the Securities, the right, which is absolute and unconditional, of
the Holder of any Security to convert such Security in accordance with Article
XIII.


                                  ARTICLE XIII

                            Conversion of Securities

                 SECTION 13.01.  Conversion Privilege and Conversion Price.
Subject to and upon compliance with the provisions of this Article XIII, at the
option of the Holder thereof, any Security or any portion of the principal
amount thereof which is U.S.$1,000 or an integral multiple of U.S.$1,000 may be
converted at the principal amount thereof, or of such portion thereof, into
fully paid and nonassessable shares of Common Stock of the Company at any time
following the latest date of original issuance of Securities at the conversion
price, determined as hereinafter provided, in effect at the time of conversion.
Such conversion right shall expire at the close of business on the Business Day
immediately preceding December 15, 2006, subject, in the case of conversion of
any Global Security, to any Applicable Procedures.  In case a Security or
portion thereof is called for redemption at the election of the Company or the
Holder thereof exercised his right to require the Company to repurchase the
Security, such conversion right in respect of the Security or portion so called
shall expire at the close of business, New York or time, on the Business Day
immediately preceding the corresponding Redemption Date or Repurchase Date, as
the case may be, unless the Company defaults in making the payment due upon
redemption or repurchase, as the case may be (in each case subject as aforesaid
to any Applicable Procedures with respect to any Global Security).

                 The price at which shares of Common Stock shall be delivered
upon conversion (herein called the "conversion price") shall be initially
U.S.$143.25 per share of Common Stock.  The conversion price shall be adjusted
in certain instances as provided in Section 13.04.

                 In case the Company shall, by dividend or otherwise, declare
or make a distribution on its Common Stock referred to in paragraph (4) or (5)
of Section 13.04 (including, without limitation, dividends or distributions
referred to in the last sentence of paragraph (4) of Section 13.04), the Holder
of each Security, upon the conversion thereof pursuant to this Article XIII
subsequent to the close of business on the date fixed for the determination of
shareholders entitled to receive such distribution and prior to the
effectiveness of the conversion price adjustment in respect of such
distribution pursuant
<PAGE>   75
                                                                              69




to paragraph (4) or (5) of Section 13.04, shall also be entitled to receive for
each share of Common Stock into which such Security is converted, the portion
of the evidences of indebtedness, shares of capital stock, securities, cash and
other property so distributed applicable to one share of Common Stock;
provided, however, that, at the election of the Company (whose election shall
be evidenced by a Board Resolution) with respect to all Holders so converting,
the Company may, in lieu of distributing to such Holder any portion of such
distribution not consisting of cash or securities of the Company, pay such
Holder an amount in cash equal to the fair market value thereof (as determined
in good faith by the Board of Directors, whose determination shall be
conclusive and described in a Board Resolution).  If any conversion of a
Security described in the immediately preceding sentence occurs prior to the
payment date for a distribution to holders of Common Stock which the Holder of
the Security so converted is entitled to receive in accordance with the
immediately preceding sentence, the Company may elect (such election to be
evidenced by a Board Resolution) to distribute to such Holder a due bill for
the evidences of indebtedness, shares of capital stock, securities, cash or
assets to which such Holder is so entitled; provided that such due bill (i)
meets any applicable requirements of the principal national securities exchange
or other market on which the Common Stock is then traded and (ii) requires
payment or delivery of such evidences of indebtedness, shares of capital stock,
securities, cash or assets no later than the date of payment or delivery
thereof to holders of Common Stock receiving such distribution.

                 SECTION 13.02.  Exercise of Conversion Privilege.  In order to
exercise the conversion privilege, the Holder of any Security to be converted
shall surrender such Security, duly endorsed or assigned to the Company or in
blank, at any office or agency maintained by the Company pursuant to Section
10.02, accompanied by (a) written notice (as set forth in Section 2.05 herein)
to the Company at such office or agency that the Holder elects to convert such
Security or, if less than the entire principal amount thereof is to be
converted, the portion thereof to be converted and (b) if shares or any portion
of such Security not to be converted are to be issued in the name of a Person
other than the Holder thereof, and the restrictions on transfer of such
Security, set forth in the first paragraph of Section 2.02 remain in effect, a
certification of the Holder as to compliance with such restrictions (as set
forth in Section 2.06).

                 If the restrictions on transfer of a Security set forth in the
first paragraph of Section 2.02 remain in effect, all shares of Common Stock
delivered upon conversion thereof shall bear a restrictive legend substantially
in the form of such paragraph.

                 Except as described in the last paragraph of Section 3.07, no
Holder of Securities will be entitled upon conversion thereof to any payment or
adjustment on account of accrued and unpaid interest thereon or on account of
dividends on the shares of Common Stock issued in connection therewith.
Securities surrendered for conversion during the period from the close of
business on any Regular Record Date to the opening of business on the
corresponding Interest Payment Date (except Securities called for redemption on
a Redemption Date within such period between and including such Regular Record
Date and such Interest Payment Date) must be accompanied by payment to the
Company in New York Clearing House Funds or other funds acceptable to the
Company of an amount equal to the interest payable on such Interest Payment
Date on the principal amount converted.

                 Securities shall be deemed to have been converted immediately
prior to the close of business on the day of surrender of such Securities for
conversion in accordance
<PAGE>   76
                                                                              70




with the foregoing provisions, and at such time the rights of the Holders of
such Securities as Holders shall cease, and the Person or Persons entitled to
receive the Common Stock issuable upon conversion shall be treated for all
purposes as the record holder or holders of such Common Stock at such time.  As
promptly as practicable on or after the conversion date, the Company shall
issue and shall deliver at such office or agency a certificate or certificates
for the number of full shares of Common Stock issuable upon conversion,
together with payment in lieu of any fraction of a share as provided in Section
13.03.

                 In the case of any Security which is converted in part only,
upon such conversion the Company shall execute and the Trustee shall
authenticate and deliver to the Holder thereof, at the expense of the Company,
a new Security or Securities of authorized denominations in aggregate principal
amount equal to the unconverted portion of the principal amount of such
Security.  Any requirements for notice, surrender or delivery of Securities
pursuant to this Article XIII shall, with respect to any Global Security, be
subject to any Applicable Procedures.

                 SECTION 13.03.  Fractions of Shares.  No fractional shares of
Common Stock shall be issued upon conversion of Securities.  If more than one
Security shall be surrendered for conversion at one time by the same Holder,
the number of full shares which shall be issuable upon conversion thereof shall
be computed on the basis of the aggregate principal amount of the Securities
(or specified portions thereof) so surrendered.  Instead of any fractional
share of Common Stock which would otherwise be issuable upon conversion of any
Security or Securities (or specified portions thereof), the Company shall pay a
cash adjustment in respect of such fraction in an amount equal to the same
fraction of the Closing Price per share of the Common Stock at the close of
business on the day of conversion (or, if such day is not a Trading Day, on the
Trading Day immediately preceding such day) or, alternatively, the Company
shall round up to the next higher whole share.

                 SECTION 13.04.  Adjustment of Conversion Price.  (1) In case
the Company shall pay or make a dividend or other distribution on its Common
Stock exclusively in Common Stock, the conversion price in effect at the
opening of business on the day next following the date fixed for the
determination of shareholders entitled to receive such dividend or other
distribution shall be reduced by multiplying such conversion price by a
fraction of which the numerator shall be the number of shares of Common Stock
outstanding at the close of business on the date fixed for such determination
and the denominator shall be the sum of such number of shares and the total
number of shares constituting such dividend or other distribution, such
reduction to become effective immediately after the opening of business on the
day next following the date fixed for such determination.  For the purposes of
this paragraph (1), the number of shares of Common Stock at any time
outstanding shall not include shares held in the treasury of the Company but
shall include shares issuable in respect of scrip certificates issued in lieu
of fractions of shares of Common Stock.  The Company shall not pay any dividend
or make any distribution on shares of Common Stock held in the treasury of the
Company.

                 (2)  In case the Company shall pay or make a dividend or other
distribution on its Common Stock consisting exclusively of, or shall otherwise
issue to all holders of its Common Stock, rights, warrants or options entitling
the holders thereof to subscribe for or purchase shares of Common Stock at a
price per share less than the current market
<PAGE>   77
                                                                              71




price per share (determined as provided in paragraph (7) of this Section 13.04)
of the Common Stock on the date fixed for the determination of shareholders
entitled to receive such rights, warrants or options, the conversion price in
effect at the opening of business on the day following the date fixed for such
determination shall be reduced by multiplying such conversion price by a
fraction of which the numerator shall be the number of shares of Common Stock
outstanding at the close of business on the date fixed for such determination
plus the number of shares of Common Stock which the aggregate of the offering
price of the total number of shares of Common Stock so offered for subscription
or purchase would purchase at such current market price and the denominator
shall be the number of shares of Common Stock outstanding at the close of
business on the date fixed for such determination plus the number of shares of
Common Stock so offered for subscription or purchase, such reduction to become
effective immediately after the opening of business on the day following the
date fixed for such determination.  For the purposes of this paragraph (2), the
number of shares of Common Stock at any time outstanding shall not include
shares held in the treasury of the Company but shall include shares issuable in
respect of scrip certificates issued in lieu of fractions of shares of Common
Stock.  The Company shall not issue any rights, warrants or options in respect
of shares of Common Stock held in the treasury of the Company.

                 (3)  In case outstanding shares of Common Stock shall be
subdivided into a greater number of shares of Common Stock, the conversion
price in effect at the opening of business on the day following the day upon
which such subdivision becomes effective shall be proportionately reduced, and,
conversely, in case outstanding shares of Common Stock shall each be combined
into a smaller number of shares of Common Stock, the conversion price in effect
at the opening of business on the day following the day upon which such
combination becomes effective shall be proportionately increased, such
reduction or increase, as the case may be, to become effective immediately
after the opening of business on the day following the day upon which such
subdivision or combination becomes effective.

                 (4)  Subject to the last sentence of this paragraph (4), in
case the Company shall, by dividend or otherwise, distribute to all holders of
its Common Stock evidences of its indebtedness, shares of any class of capital
stock, securities, cash or property (excluding any rights, warrants or options
referred to in paragraph (2) of this Section 13.04, any dividend or
distribution paid exclusively in cash and any dividend or distribution referred
to in paragraph (1) of this Section 13.04), the conversion price shall be
reduced so that the same shall equal the price determined by multiplying the
conversion price in effect immediately prior to the effectiveness of the
conversion price reduction contemplated by this paragraph (4) by a fraction of
which the numerator shall be the current market price per share (determined as
provided in paragraph (7) of this Section 13.04) of the Common Stock on the date
of such effectiveness less the fair market value (as determined in good faith by
the Board of Directors, whose determination shall be conclusive and described in
a Board Resolution and shall, in the case of securities being distributed for
which prior thereto there is an actual or when issued trading market, be no less
than the value determined by reference to the average of the closing prices in
such market over the period specified in the succeeding sentence), on the date
of such effectiveness, of the portion of the evidences of indebtedness, shares
of capital stock, securities, cash and property so distributed applicable to one
share of Common Stock and the denominator shall be such current market price per
share of the Common Stock, such reduction to become effective immediately prior
to the opening of business on the day next following the later of (a) the date
fixed for the payment of such distribution and
<PAGE>   78
                                                                              72



(b) the date 20 days after the notice relating to such distribution is given
pursuant to Section 13.06(a) (such later date of (a) and (b) being referred to
as the "Reference Date").  If the Board of Directors determines the fair market
value of any distribution for purposes of this paragraph (4) by reference to
the actual or when issued trading market for any securities comprising such
distribution, it must in doing so consider the prices in such market over the
same period used in computing the current market price per share pursuant to
paragraph (7) of this Section.  For purposes of this paragraph (4), any
dividend or distribution that includes shares of Common Stock or rights,
warrants or options to subscribe for or purchase shares of Common Stock shall
be deemed instead to be (a) a dividend or distribution of the evidences of
indebtedness, cash, property, shares of capital stock or securities other than
such shares of Common Stock or such rights, warrants or options (making any
conversion price reduction required by this paragraph (4)) immediately followed
by (b) a dividend or distribution of such shares of Common Stock or such rights
(making any further conversion price reduction required by paragraph (1) or (2)
of this Section 13.04, except (i) the Reference Date of such dividend or
distribution as defined in this paragraph (4) shall be substituted as "the date
fixed for the determination of shareholders entitled to receive such dividend
or other distributions", "the date fixed for the determination of shareholders
entitled to receive such rights, warrants or options" and "the date fixed for
such determination" within the meaning of paragraphs (1) and (2) of this
Section 13.04 and (ii) any shares of Common Stock included in such dividend or
distribution shall not be deemed "outstanding at the close of business on the
date fixed for such determination" within the meaning of paragraph (1) of this
Section 13.04).

                 (5)  In case the Company shall, by dividend or otherwise, make
a distribution to all holders of its Common Stock exclusively in cash in an
aggregate amount that, together with (i) the aggregate amount of any other
distributions to all holders of its Common Stock made exclusively in cash
within the 12 months preceding the date of payment of such distribution and in
respect of which no conversion price adjustment pursuant to this paragraph (5)
has been made and (ii) the aggregate of any cash plus the fair market value (as
determined in good faith by the Board of Directors, whose determination shall
be conclusive and described in a Board Resolution), as of the expiration of the
tender or exchange offer referred to below, of consideration payable in respect
of any tender or exchange offer by the Company or a Subsidiary for all or any
portion of the Common Stock concluded within the 12 months preceding the date
of payment of such distribution and in respect of which no conversion price
adjustment pursuant to paragraph (6) of this Section 13.04 has been made,
exceeds 12.5% of the product of the current market price per share (determined
as provided in paragraph (7) of this Section 13.04) of the Common Stock on the
date fixed for shareholders entitled to receive such distribution times the
number of shares of Common Stock outstanding on such date, the conversion price
shall be reduced so that the same shall equal the price determined by
multiplying the conversion price in effect immediately prior to the
effectiveness of the conversion price reduction contemplated by this paragraph
(5) by a fraction of which the numerator shall be the current market price per
share (determined as provided in paragraph (7) of this Section 13.04) of the
Common Stock on the date of such effectiveness less the amount of cash so
distributed applicable to one share of Common Stock and the denominator shall
be such current market price per share of the Common Stock, such reduction to
become effective immediately prior to the opening of business on the later of
(a) the day following the date fixed for the payment of such distribution and
(b) the date 20 days after the notice relating to such distribution is given
pursuant to Section 13.06(a).

<PAGE>   79
                                                                              73


                 (6)  In case a successful tender or exchange offer made by the
Company or any Subsidiary for all or any portion of the Common Stock shall
involve an aggregate consideration having a fair market value (as determined in
good faith by the Board of Directors, whose determination shall be conclusive
and described in a Board Resolution) at the last time (the "Expiration Time")
tenders or exchanges may be made pursuant to such tender or exchange offer (as
it may be amended) that, together with (i) the aggregate of the cash plus the
fair market value (as determined in good faith by the Board of Directors, whose
determination shall be conclusive and described in a Board Resolution), as of
the expiration of the other tender or exchange offer referred to below, of
consideration payable in respect of any other tender or exchange offer by the
Company or a Subsidiary for all or any portion of the Common Stock concluded
within the preceding 12 months and in respect of which no conversion price
adjustment pursuant to this paragraph (6) has been made and (ii) the aggregate
amount of any distributions to all holders of the Common Stock made exclusively
in cash within the preceding 12 months and in respect of which no conversion
price adjustment pursuant to paragraph (5) of this Section 13.04 has been made,
exceeds 12.5% of the product of the current market price per share (determined
as provided in paragraph (7) of this Section 13.04) of the Common Stock on the
Expiration Time times the number of shares of Common Stock outstanding
(including any tendered shares) on the Expiration Time, the conversion price
shall be reduced (but not increased) so that the same shall equal the price
determined by multiplying the conversion price in effect immediately prior to
the Expiration Time by a fraction of which the numerator shall be (i) the
product of the current market price per share (determined as provided in
paragraph (7) of this Section 13.04) of the Common Stock at the Expiration Time
times the number of shares of Common Stock outstanding (including any tendered
or exchanged shares) at the Expiration Time minus (ii) the fair market value
(determined as aforesaid) of the aggregate consideration payable to
shareholders based on the acceptance (up to any maximum specified in the terms
of the tender or exchange offer) of all shares validly tendered or exchanged
and not withdrawn as of the Expiration Time (the shares deemed so accepted, up
to any such maximum, being referred to as the "Purchased Shares") and the
denominator shall be the product of (i) such current market price per share at
the Expiration Time times (ii) such number of outstanding shares at the
Expiration Time less the number of Purchased Shares, such reduction to become
effective immediately prior to the opening of business on the day following the
Expiration Time.

                 (7)  For the purpose of any computation under this paragraph
and paragraphs (2), (4) and (5) of this Section 13.04, the current market price
per share of Common Stock on any date in question shall be deemed to be the
average of the daily Closing Prices for the 5 consecutive Trading Days selected
by the Company commencing not more than 20 Trading Days before, and ending not
later than, the date in question; provided, however, that (i) if the "ex" date
(as hereinafter defined) for any event (other than the issuance or distribution
requiring such computation) that requires an adjustment to the conversion price
pursuant to paragraph (1), (2), (3), (4), (5) or (6) above ("Other Event")
occurs on or after the 20th Trading Day prior to the date in question and prior
to the "ex" date for the issuance or distribution requiring such computation
(the "Current Event"), the Closing Price for each Trading Day prior to the "ex"
date for such Other Event shall be adjusted by multiplying such Closing Price
by the same fraction by which the conversion price is so required to be
adjusted as a result of such Other Event, (ii) if the "ex" date for any Other
Event occurs after the "ex" date for the Current Event and on or prior to the
date in question, the Closing Price for each Trading Day on and after the "ex"
date for such Other Event shall be adjusted by multiplying such Closing Price
by the

<PAGE>   80
                                                                              74


reciprocal of the fraction by which the conversion price is so required to be
adjusted as a result of such Other Event, (iii) if the "ex" date for any Other
Event occurs on the "ex" date for the Current Event, one of those events shall
be deemed for purposes of clauses (i) and (ii) of this proviso to have an "ex"
date occurring prior to the "ex" date for the other event, and (iv) if the "ex"
date for the Current Event is on or prior to the date in question, after taking
into account any adjustment required pursuant to clause (ii) of this proviso,
the Closing Price for each Trading Day on or after such "ex" date shall be
adjusted by adding thereto the amount of any cash and the fair market value on
the date in question (as determined in good faith by the Board of Directors in
a manner consistent with any determination of such value for purposes of
paragraph (4) or (5) of this Section 13.04, whose determination shall be
conclusive and described in a Board Resolution) of the portion of the rights,
warrants, options, evidences of indebtedness, shares of capital stock,
securities, cash or property being distributed applicable to one share of
Common Stock.  For the purpose of any computation under paragraph (6) of this
Section 13.04, the current market price per share of Common Stock on any date
in question shall be deemed to be the average of the daily Closing Prices for
the 5 consecutive Trading Days selected by the Company commencing on or after
the latest (the "Commencement Date") of (i) the date 20 Trading Days before the
date in question, (ii) the date of commencement of the tender or exchange offer
requiring such computation and (iii) the date of the last amendment, if any, of
such tender or exchange offer involving a change in the maximum number of
shares for which tenders are sought or a change in the consideration offered,
and ending not later than the date of the Expiration Time of such tender or
exchange offer (or, if such Expiration Time occurs before the close of trading
on a Trading Day, not later than the Trading Day immediately preceding the date
of such Expiration Time); provided, however, that if the "ex" date for any
Other Event (other than the tender or exchange offer requiring such
computation) occurs on or after the Commencement Date and on or prior to the
date of the Expiration Time for the tender or exchange offer requiring such
computation, the Closing Price for each Trading Day prior to the "ex" date for
such Other Event shall be adjusted by multiplying such Closing Price by the
same fraction by which the conversion price is so required to be adjusted as a
result of such other event.  For purposes of this paragraph, the term "ex"
date, (i) when used with respect to any issuance or distribution, means the
first date on which the Common Stock trades regular way on the relevant
exchange or in the relevant market from which the Closing Price was obtained
without the right to receive such issuance or distribution, (ii) when used with
respect to any subdivision or combination of shares of Common Stock, means the
first date on which the Common Stock trades regular way on such exchange or in
such market after the time at which such subdivision or combination becomes
effective, and (iii) when used with respect to any tender or exchange offer
means the first date on which the Common Stock trades regular way on such
exchange or in such market after the Expiration Time of such tender or exchange
offer.

                 (8)  The Company may make such reductions in the conversion
price, in addition to those required by paragraphs (1), (2), (3), (4), (5) and
(6) of this Section, as it considers to be advisable in order that any event
treated for Federal income tax purposes as a dividend of stock or stock rights
shall not be taxable to the recipients, or to diminish the amount of such tax
payable.

                 (9)  No adjustment in the conversion price shall be required
unless such adjustment would require an increase or decrease of at least 1% in
the conversion price; provided, however, that any adjustments which by reason
of this paragraph (9) are not

<PAGE>   81
                                                                              75


required to be made shall be carried forward and taken into account in any
subsequent adjustment.

                 (10)  In the event that the Company distributes rights or
warrants (other than those referred to in paragraph (2) above) pro rata to
holders of Common Stock, so long as any such rights or warrants have not
expired or been redeemed by the Company, the Company shall make proper
provision so that the Holder of any Security surrendered for conversion will be
entitled to receive upon such conversion, in addition to the Conversion Shares,
a number of rights and warrants to be determined as follows:  (i) if such
conversion occurs on or prior to the date for the distribution to the holders
of rights or warrants of separate certificates evidencing such rights or
warrants (the "Distribution Date"), the same number of rights or warrants to
which a holder of a number of shares of Common Stock equal to the number of
Conversion Shares is entitled at the time of such conversion in accordance with
the terms and provisions of and applicable to the rights or warrants, and (ii)
if such conversion occurs after such Distribution Date, the same number of
rights or warrants to which a holder of the number of shares of Common Stock
into which the principal amount of such Security so converted was convertible
immediately prior to such Distribution Date would have been entitled on such
Distribution Date in accordance with the terms and provisions of and applicable
to the rights or warrants.

                 SECTION 13.05.  Notice of Adjustments of Conversion Price.
Whenever the conversion price is adjusted as herein provided:

                 (a) the Company shall compute the adjusted conversion price in
     accordance with Section 13.04 and shall prepare a certificate signed by
     the Treasurer of the Company setting forth the adjusted conversion price
     and showing in reasonable detail the facts upon which such adjustment is
     based, and such certificate shall forthwith be filed (with a copy to the
     Trustee) at each office or agency maintained for the purpose of conversion
     of Securities pursuant to Section 10.02; and

                 (b) a notice stating that the conversion price has been
     adjusted and setting forth the adjusted conversion price shall forthwith
     be required, and as soon as practicable after it is required, such notice
     shall be mailed by the Company to all Holders at their last addresses as
     they shall appear in the Security Register.

                 SECTION 13.06.  Notice of Certain Corporate Action.  In case:

                 (a) the Company shall declare a dividend (or any other
     distribution) on its Common Stock that would require a conversion price
     adjustment pursuant to paragraph (5) of Section 13.04; or

                 (b) the Company shall authorize the granting to all holders of
     its Common Stock of rights, warrants or options to subscribe for or
     purchase any shares of capital stock of any class or of any other rights
     (excluding rights distributed pursuant to any shareholder rights plan); or

                 (c) of any reclassification of the Common Stock of the Company
     (other than a subdivision or combination of its outstanding shares of
     Common Stock), or of any consolidation or merger to which the Company is a
     party and for which approval

<PAGE>   82
                                                                              76



     of any shareholders of the Company is required, or of the sale or transfer
     of all or substantially all of the assets of the Company; or

                 (d) of the voluntary or involuntary dissolution, liquidation or
     winding, up of the Company; or

                 (e) the Company or any Subsidiary of the Company shall
     commence a tender or exchange offer for all or a portion of the Company's
     outstanding shares of Common Stock (or shall amend any such tender or
     exchange offer);

then the Company shall cause to be filed at each office or agency maintained
for the purpose of conversion of Securities pursuant to Section 10.02, and
shall cause to be mailed to all Holders at their last addresses as they shall
appear in the Security Register, at least 20 days (or 10 days in any case
specified in clause (a) or (b) above) prior to the applicable record, effective
or expiration date hereinafter specified, a notice stating (x) the date on
which a record is to be taken for the purpose of such dividend, distribution or
granting of rights, warrants or options, or, if a record is not to be taken,
the date as of which the holders of Common Stock of record to be entitled to
such dividend, distribution, rights, warrants or options are to be determined,
or (y) the date on which such reclassification, consolidation, merger, sale,
transfer, dissolution, liquidation or winding up is expected to become
effective, and the date as of which it is expected that holders of Common Stock
of record shall be entitled to exchange their shares of Common Stock for
securities, cash or other property deliverable upon such reclassification,
consolidation, merger, sale, transfer, dissolution, liquidation or winding up,
or (z) the date on which such tender offer commenced, the date on which such
tender offer is scheduled to expire unless extended, the consideration offered
and the other material terms thereof (or the material terms of any amendment
thereto).

                 SECTION 13.07.  Company to Reserve Common Stock.  The Company
shall at all times reserve and keep available, free from preemptive rights, out
of its authorized but unissued Common Stock, solely for the purpose of
effecting the conversion of Securities, the whole number of shares of Common
Stock then issuable upon the conversion in full of all outstanding Securities.

                 SECTION 13.08.  Taxes on Conversions. The Company will pay any
and all taxes that may be payable in respect of the issue or delivery of shares
of Common Stock on conversion of Securities pursuant hereto. The Company shall
not, however, be required to pay any tax which may be payable in respect of any
transfer involved in the issue and delivery of shares of Common Stock in a name
other than that of the Holder of the Security or Securities to be converted,
and no such issue or delivery shall be made unless and until the Person
requesting such issue has paid to the Company the amount of any such tax, or
has established to the satisfaction of the Company that such tax has been paid.

                 SECTION 13.09.  Covenant as to Common Stock.  The Company
covenants that all shares of Common Stock which may be issued upon conversion
of Securities will upon issue be newly issued (and not treasury shares) and be
duly authorized, validly issued, fully paid and nonassessable and, except as
provided in Section 13.08, the Company will pay all taxes, liens and charges
with respect to the issue thereof.

<PAGE>   83
                                                                              77


                 SECTION 13.10.  Cancellation of Converted Securities. All
Securities delivered for conversion shall be delivered to the Trustee to be
cancelled by or at the direction of the Trustee, which shall dispose of the
same as provided in Section 3.09.

                 SECTION 13.11.  Provisions in Case of Reclassification,
Consolidation, Merger or Sale of Assets.  In the event that the Company shall
be a party to any transaction (including without limitation any (i)
recapitalization or reclassification of the Common Stock (other than a change
in par value, or from par value to no par value, or from no par value to par
value, or as a result of a subdivision or combination of the Common Stock),
(ii) any consolidation of the Company with, or merger of the Company into, any
other person. any merger of another person into the Company (other than a
merger which does not result in a reclassification, conversion, exchange or
cancellation of outstanding shares of Common Stock of the Company), (iii) any
sale or transfer of all or substantially all of the assets of the Company, or
(iv) any other transaction) pursuant to which the Common Stock is converted
into the right to receive other securities, cash or other property, then lawful
provision shall be made as part of the terms of such transaction whereby the
Holder of each Security then outstanding shall have the right thereafter to
convert such Security only into (subject to funds being legally available for
such purpose under applicable law at the time of such conversion) the kind and
amount of securities, cash and other property receivable upon such transaction
by a holder of the number of shares of Common Stock into which such Security
might have been converted immediately prior to such transaction.  The Company
or the person formed by such consolidation or resulting from such merger or
which acquired such assets or which acquired the Company's shares, as the case
may be, shall execute and deliver to the Trustee a supplemental indenture
establishing such rights.  Such supplemental indenture shall provide for
adjustments which, for events subsequent to the effective date of such
supplemental indenture, shall be as nearly equivalent as may be practicable to
the adjustments provided for in this Article.  The above provisions of this
Section 13.11 shall similarly apply to successive transactions of the foregoing
type.

                                  ARTICLE XIV

                          Right to Require Repurchase

                 SECTION 14.01.  Right to Require Repurchase.  In the event
that there shall occur a Change in Control (as defined in Section 14.06), then
each Holder shall have the right, at such Holder's option, to require the
Company, subject to the provisions of Section 12.03, to purchase all or any
designated part of such Holder's Securities on the date (the "Repurchase Date")
fixed by the Company that is not less than 30 days nor more than 45 days after
the date the Company gives notice of the Change in Control as contemplated in
Section 14.02(a) at a price (the "Repurchase Price") equal to 100% of the
principal amount thereof, together with accrued and unpaid interest through the
Repurchase Date. Such right to require the repurchase of Securities shall not
continue after a discharge of the Company from its obligations with respect to
the Securities in accordance with Article IV.  Any requirements for notice,
surrender or delivery of Securities pursuant to this Article XIV shall, with
respect to any Global Security, be subject to any Applicable Procedures.

                 SECTION 14.02.  Notice, Method of Exercising Repurchase Right.
(a)  On or before the 15th day after the Company knows or reasonably should
know a Change

<PAGE>   84
                                                                              78


in Control has occurred, the Company, or at the written request of the Company,
the Trustee (in the name and at the expense of the Company), shall give notice
of the occurrence of the Change in Control and of the repurchase right set
forth herein arising as a result thereof by first-class mail, postage prepaid,
or by telefacsimile with written acknowledgment of transmittal to each Holder
of the Securities at such Holder's address appearing in the Security Register.
The Company shall also deliver a copy of such notice of a repurchase right to
the Trustee.

                 Each notice of a repurchase right shall state:

                 (1) the Repurchase Date,

                 (2) the date by which the repurchase right must be exercised,

                 (3) the Repurchase Price, and

                 (4) the instructions a Holder must follow to exercise its
                     repurchase right.

                 No failure of the Company to give the foregoing notice shall
limit any Holder's right to exercise a repurchase right. The Trustee shall have
no affirmative obligation to determine if there shall have occurred a Change in
Control.

                 (b)  To exercise a repurchase right, a Holder shall deliver to
the Company (or an agent designated by the Company for such purpose in the
notice referred to in (a) above) and to the Trustee on or before the 30th day
after the date of transmittal of the notice referred to in (a) above (i)
written notice of the Holder's exercise of such right, which notice shall set
forth the name of the Holder, the principal amount of the Security or
Securities (or portion of a Security) to be repurchased, and a statement that
an election to exercise the repurchase right is being made thereby, and (ii)
the Security or Securities with respect to which the repurchase right is being
exercised, duly endorsed for transfer to the Company. Such written notice shall
be irrevocable. If the Repurchase Date falls between any Regular Record Date
and the corresponding succeeding Interest Payment Date, Securities to be
repurchased must be accompanied by payment from the Holder of an amount equal
to the interest thereon which the registered Holder thereof is to receive on
such Interest Payment Date.

                 (c)  In the event a repurchase right shall be exercised in
accordance with the terms hereof, the Company shall on the Repurchase Date pay
or cause to be paid in cash to the Holder thereof the Repurchase Price of the
Security or Securities as to which the repurchase right had been exercised.

                 SECTION 14.03.  Deposit of Repurchase Price.  On or prior to
the Repurchase Date, the Company shall deposit with the Trustee or with a
Paying Agent (or, if the Company is acting as its own Paying Agent, segregate
and hold in trust as provided in Section 10.03) an amount of money sufficient
to pay the Repurchase Price of the Securities which are to be repaid on the
Repurchase Date.

                 SECTION 14.04.  Securities Not Repurchased on Repurchase Date.
If any Security surrendered for repurchase shall not be so paid on the
Repurchase Date, the principal of such Security shall, until paid, bear
interest from the Repurchase Date at a rate borne by such Security.

<PAGE>   85
                                                                              79


                 SECTION 14.05.  Securities Repurchased in Part.  Any Security
which is to be repurchased only in part shall be surrendered at any office or
agency of the Company designated for that purpose pursuant to Section 10.02
(with, if the Company or the Trustee so requires, due endorsement by, or
written instrument of transfer in form satisfactory to the Company and the
Trustee duly executed by, the Holder thereof or his attorney duly authorized in
writing), and the Company shall execute, and the Trustee shall authenticate and
deliver to the Holder of such Security without service charge, a new Security
or Securities of any authorized denomination as requested by such Holder, in
aggregate principal amount equal to and in exchange for the unrepurchased
portion of the principal of the Security so surrendered.

                 SECTION 14.06.  Certain Definitions.  For purposes of this
Article:  The term "Beneficial Owner" shall be determined in accordance with
Rules 13d-3 and 13d-5 promulgated by the Commission under the Exchange Act, or
any successor provision thereto, except that a Person shall be deemed to have
"beneficial ownership" of all shares that such Person has the right to acquire,
whether such right is exercisable immediately or only after the passage of
time.

                 A "Change in Control" shall be deemed to have occurred at such
time as (a) any Person, or any Persons acting together in a manner which would
constitute a "group" (a "Group") for purposes of Section 13(d) of the Exchange
Act, or any successor provision thereto, together with any Affiliates thereof,
(i) become the Beneficial Owners, directly or indirectly, of capital stock of
the Company, entitling such Person or Persons and its or their Affiliates to
exercise more than 50% of the total voting power of all classes of the
Company's capital stock entitled to vote generally in the election of directors
or (ii) shall succeed in having sufficient of its or their nominees (who are
not supported by a majority of the then current Board of Directors of the
Company) elected to the Board of Directors of the Company such that such
nominees, when added to any existing directors remaining on the Board of
Directors of the Company after such election who are Affiliates of or acting in
concert with any such Persons, shall constitute a majority of the Board of
Directors of the Company, (b) the Company shall be a party to any transaction
pursuant to which the Common Stock is converted into the right to receive other
securities (other than common stock), cash and/or property (or the Company, by
dividend, tender or exchange offer or otherwise, distributes other securities,
cash and/or property to holders of Common Stock) and the value of all such
securities, cash and/or property distributed in such transaction and any other
transaction effected within the 12 months preceding consummation of such
transaction (as determined in good faith by the Board of Directors, whose
determination shall be conclusive and described in a Board Resolution) is more
than 50% of the average of the daily Closing Prices for the five consecutive
Trading Days ending on the Trading Day immediately preceding the date of such
transaction (or, if earlier, the Trading Day immediately preceding the "ex"
date (as defined in paragraph (7) of Section 13.04) for such transaction) or
(c) the Company shall consolidate with or merge into any other Person or sell,
convey, transfer or lease its properties and assets substantially as an
entirety to any Person other than a Subsidiary, or any other Person shall
consolidate with or merge into the Company (other than, in the case of this
clause (c), pursuant to any consolidation or merger where Persons who are
shareholders of the Company immediately prior thereto become the Beneficial
Owners of shares of capital stock of the surviving company entitling such
Persons to exercise more than 50% of the total voting power of all classes of
such surviving company's capital stock entitled to vote generally in the
election of directors).

<PAGE>   86
                                                                              80



                 Notwithstanding the foregoing, a "Change in Control" will be
deemed not to have occurred (i) if the Closing Price of the Common Stock for
any five Trading Days during the ten Trading Days immediately preceding the
Change in Control is at least equal to 105% of the conversion price in effect
immediately preceding the Change in Control or (ii) if at least 90% of the
consideration (excluding cash payments for fractional shares or cash payments
for appraisal rights) received or to be received by the shareholders of the
Company in the transaction or transactions constituting the Change in Control
consists of (x) shares of common stock or securities convertible into such
shares of common stock, of an entity organized and validly existing under the
laws of the United States of America, any State thereof or the District of
Columbia the common stock of which is, or upon issuance will be, traded on a
national securities exchange in the United States of America or through Nasdaq
or (y) shares of common stock of an entity organized and validly existing under
the laws of a jurisdiction outside of the United States of America, or American
Depositary Shares representing such shares of common stock, that are, or upon
issuance will be, traded on a national securities exchange in the United States
of America or through Nasdaq, if such entity has an average worldwide total
market capitalization of its equity securities of at least U.S. $5 billion
during the ten Trading Days immediately preceding the date of the Change in
Control.

                                   ARTICLE XV

                       Defeasance and Covenant Defeasance

                 SECTION 15.01.  Company's Option to Effect Defeasance or
Covenant Defeasance.  The Company may at its option by Board Resolution, at any
time, elect to have either Section 15.02 or Section 15.03 applied to the
Outstanding Securities upon compliance with the conditions set forth below in
this Article XV.

                 SECTION 15.02.  Defeasance and Discharge. Upon the Company's
exercise of the option provided in Section 15.01 applicable to this Section,
the Company shall be deemed to have been discharged from its obligations with
respect to the Outstanding Securities (other than those specified below), the
Holders and any holders of Senior Indebtedness, and the provisions of Article
XII hereof shall cease to be effective, on the date the conditions set forth
below are satisfied (hereinafter, "defeasance"). For this purpose, such
defeasance means that the Company shall be deemed to have paid and discharged
the entire indebtedness represented by the Outstanding Securities, the Company
shall be deemed to have satisfied all their other obligations under such
Securities and this Indenture insofar as such Securities are concerned (and the
Trustee, at the expense of the Company, shall execute proper instruments
acknowledging the same), except for the following which shall survive until
otherwise terminated or discharged hereunder:  (A) the rights of Holders of
such Securities to receive, solely from the trust fund described in Section
15.04 and as more fully set forth in such Section, payments in respect of the
principal of, premium, if any (including the Make-Whole Payment, if any), and
interest on such Securities when such payments are due, (B) the Company's
obligations with respect to such Securities under Sections 3.04, 3.05, 3.06,
10.02, 10.03, 10.11, Article XIII and Article XIV, (C) the rights, powers,
trusts, duties and immunities of the Trustee hereunder and (D) this Article XV.
Subject to compliance with this Article XV, the Company may exercise its option
under this Section 15.02 notwithstanding the prior exercise of its option under
Section 15.03.
<PAGE>   87
                                                                              81



                 SECTION 15.03.  Covenant Defeasance.  Upon the Company's
exercise of the option provided in Section 15.01 applicable to this Section,
(i) the Company shall be released from its obligations under Section 10.06 and
Section 10.07, (ii) the occurrence of an event specified in Section 5.01(4)
(with respect to either of Section 10.06 or Section 10.07) or 5.01(5) shall not
be deemed to be an Event of Default and (iii) the provisions of Article XII
hereof shall cease to be effective on and after the date the conditions set
forth below are satisfied (hereinafter, "covenant defeasance"). For this
purpose, such covenant defeasance means that the Company may omit to comply
with and shall have no liability in respect of any term, condition or
limitation set forth in any such Section or Article, whether directly or
indirectly by reason of any reference elsewhere herein to any such Section or
Article or by reason of any reference in any such Section or Article to any
other provision herein or in any other document, but the remainder of this
Indenture and such Securities shall be unaffected thereby.

                 SECTION 15.04.  Conditions to Defeasance or Covenant
Defeasance.  The following shall be the conditions to application of either
Section 15.02 or Section 15.03 to the then Outstanding Securities:

                 (1)  The Company shall irrevocably have deposited or caused to
     be deposited with the Trustee (or another trustee satisfying the
     requirements of Section 6.09 who shall agree to comply with the provisions
     of this Article XV applicable to it) as trust funds in trust for the
     purpose of making the following payments, specifically pledged as security
     for, and dedicated solely to, the benefit of the Holders of such
     Securities, (A) money in an amount, or (B) U.S. Government Obligations
     which through the scheduled payment of principal and interest in respect
     thereof in accordance with their terms will provide, not later than one
     day before the due date of any payment, money in an amount, or (C) a
     combination thereof, sufficient, in the written opinion of a nationally
     recognized firm of independent public accountants expressed in a written
     certification thereof delivered to the Trustee, to pay and discharge, and
     which shall be applied by the Trustee (or other qualifying trustee) to pay
     and discharge, the principal of, premium, if any (including the Make-Whole
     Payment, if any), and each installment of interest on the Securities on
     the Stated Maturity of such principal or installment of interest in
     accordance with the terms of this Indenture and of such Securities. For
     this purpose, "U.S. Government Obligations" means securities that are (x)
     direct obligations of the United States of America for the payment of
     which its full faith and credit is pledged or (y) obligations of a Person
     controlled or supervised by and acting as an agency or instrumentality of
     the United States of America the payment of which is unconditionally
     guaranteed as a full faith and credit obligation by the United States of
     America, which, in either case, are not callable or redeemable at the
     option of the issuer thereof, and shall also include a depository receipt
     issued by a bank (as defined in Section 3(a)(2) of the Securities Act) as
     custodian with respect to any such U.S. Government Obligation or a
     specific payment of principal of or interest on any such U.S. Government
     Obligation held by such custodian for the account of the holder of such
     depository receipt; provided that (except as required by law) such
     custodian is not authorized to make any deduction from the amount payable
     to the holder of such depository receipt from any amount received by the
     custodian in respect of the U.S. Government Obligation or the specific
     payment of principal of or interest on the U.S. Government Obligation
     evidenced by such depository receipt.

<PAGE>   88
                                                                              82



                 (2)  In the case of an election under Section 15.02, the
     Company shall have delivered to the Trustee an Opinion of Counsel stating
     that (x) the Company has received from, or there has been published by,
     the Internal Revenue Service a ruling, or (y) since the date of this
     Indenture there has been a change in the applicable Federal income tax
     law, in either case to the effect that, and based thereon such opinion
     shall confirm that, the Holders of the Outstanding Securities will not
     recognize gain or loss for Federal income tax purposes as a result of such
     deposit, defeasance and discharge and will be subject to Federal income
     tax on the same amount, in the same manner and at the same times as would
     have been the case if such deposit, defeasance and discharge had not
     occurred.

                 (3)  In the case of an election under Section 15.03, the
     Company shall have delivered to the Trustee an Opinion of Counsel to the
     effect that the Holders of the Outstanding Securities will not recognize
     gain or loss for Federal income tax purposes as a result of such deposit
     and covenant defeasance and will be subject to Federal income tax on the
     same amount, in the same manner and at the same times as would have been
     the case if such deposit and covenant defeasance had not occurred.

                 (4)  The Company shall have delivered to the Trustee an
     Officers' Certificate to the effect that the Securities, if then listed on
     any securities exchange, will not be delisted as a result of such deposit.

                 (5)  Such defeasance or covenant defeasance shall not cause
     the Trustee to have a conflicting interest as defined in Section 6.08 and
     for purposes of the Trust Indenture Act with respect to any securities of
     the Company.

                 (6)  At the time of such deposit: (A) no default in the
     payment of all or a portion of principal of or premium, if any (including
     the Make-Whole Payment, if any), or interest on or other obligations in
     respect of any Senior Indebtedness shall have occurred and be continuing,
     and no event of default with respect to any Senior Indebtedness shall have
     occurred and be continuing and shall have resulted in such Senior
     Indebtedness becoming or being declared due and payable prior to the date
     on which it would otherwise have become due and payable and (B) no other
     event with respect to any Senior Indebtedness shall have occurred and be
     continuing permitting (after notice or the lapse of time, or both) the
     holders of such Senior Indebtedness (or a trustee on behalf of the holders
     thereof) to declare such Senior Indebtedness due and payable prior to the
     date on which it would otherwise have become due and payable, or, in the
     case of either clause (A) or clause (B) above, each such default or event
     of default shall have been cured or waived or shall have ceased to exist.

                 (7)  No Event of Default or event which with notice or lapse
     of time or both would become an Event of Default shall have occurred and
     be continuing on the date of such deposit or, insofar as subsections
     5.01(6) and (7) are concerned, at any time during the period ending on the
     121st day after the date of such deposit (it being understood that this
     condition shall not be deemed satisfied until the expiration of such
     period).

                 (8)  Such defeasance or covenant defeasance shall not result
     in a breach or violation of, or constitute a default under, any other
     agreement or instrument to which the Company is a party or by which it is
     bound.

<PAGE>   89
                                                                              83



                 (9)  The Company shall have delivered to the Trustee an
     Officers' Certificate and an Opinion of Counsel, each stating that all
     conditions precedent provided for relating to either the defeasance under
     Section 15.02 or the covenant defeasance under Section 15.03 (as the case
     may be) have been complied with.

                 (10)  Such defeasance or covenant defeasance shall not result
     in the trust arising from such deposit constituting an investment company
     as defined in the Investment Company Act of 1940, as amended, or such
     trust shall be qualified under such act or exempt from regulation
     thereunder.

                 SECTION 15.05.  Deposited Money and U.S. Government
Obligations to Be Held in Trust; Other Miscellaneous Provisions.  Subject to
the provisions of the last paragraph of Section 10.03, all money and U.S.
Government Obligations (including the proceeds thereof) deposited with the
Trustee (or other qualifying trustee collectively, for purposes of this Section
15.05, the "Trustee") pursuant to Section 15.04 in respect of the Securities
shall be held in trust and applied by the Trustee, in accordance with the
provisions of such Securities and this Indenture, to the payment, either
directly or through any Paying Agent (including the Company acting as its own
Paying Agent) as the Trustee may determine, to the Holders of such Securities,
of all sums due and to become due thereon in respect of principal, premium, if
any (including the Make-Whole Payment, if any), and interest. Money so held in
trust shall not be subject to the provisions of Article XII.

                 The Company shall pay and indemnify the Trustee against any
tax, fee or other charge imposed on or assessed against the U.S. Government
Obligations deposited pursuant to Section 15.04 or the principal and interest
received in respect thereof other than any such tax, fee or other charge which
by law is for the account of the Holders of the Outstanding Securities.

                 Anything in this Article XV to the contrary notwithstanding,
the Trustee shall deliver or pay to the Company from time to time upon Company
Request any money or U.S. Government Obligations held by it as provided in
Section 15.04 which, in the opinion of a nationally recognized firm of
independent public accountants expressed in a written certification thereof
delivered to the Trustee, are in excess of the amount thereof which would then
be required to be deposited to effect an equivalent defeasance or covenant
defeasance.

                 SECTION 15.06.  Reinstatement.  If the Trustee or the Paying
Agent is unable to apply any money in accordance with Section 15.02 or 15.03 by
reason of any order or judgment of any court or governmental authority
enjoining, restraining or otherwise prohibiting such application, then the
Company's obligations under this Indenture and the Securities shall be revived
and reinstated as though no deposit had occurred pursuant to this Article XV
until such time as the Trustee or Paying Agent is permitted to apply all such
money in accordance with Section 15.02 or 15.03; provided, however, that if the
Company makes any payment of principal of, premium, if any (including the
Make-Whole Payment, if any), or interest on any Security following the
reinstatement of its obligations, the Company shall be subrogated to the rights
of the Holders of such Securities to receive such payment from the money held
by the Trustee or the Paying Agent.

<PAGE>   90

                                                                              84





                                  ARTICLE XVI

                                    Immunity

                 SECTION 16.01.  Personal Immunity of Incorporators,
Shareholders, Directors and Officers.  No recourse for the payment of the
principal of or interest on the Securities, and no recourse under or upon any
obligation, covenant or agreement contained in this Indenture or in any
indenture supplemental hereto, or in the Securities, or because of any
indebtedness evidenced thereby, shall be had against any incorporator, or
against any past, present or future shareholder, officer or director, as such,
of the Company or any successor corporation, either directly or through the
Company or any successor corporation, under any rule of law, statute or
constitutional provision or by the enforcement of any assessment or by any
legal or equitable proceeding or otherwise, all such liability being expressly
waived and released by the acceptance of the Securities by the Holders thereof
and as part of the consideration for the issue of the Securities. Each and
every Holder of the Securities, by receiving and holding the same, agrees to
the provisions of this Section 16.01 and waives and releases any and all such
recourse, claim and liability.

<PAGE>   91


                 This instrument may be executed in any number of counterparts,
each of which so executed shall be deemed to be an original, but all such
counterparts shall together constitute but one and the same instrument.


                 IN WITNESS WHEREOF, the parties hereto have caused this
Indenture to be duly executed as of the day and year first above written.


                                        HUMAN GENOME SCIENCES, INC.

                                        by  /s/ Steven C. Mayer
                                           -----------------------------------
                                           Name:  Steven C. Mayer
                                           Title: Senior Vice President and
                                                  Chief Financial Officer

<PAGE>   92



                                    THE BANK OF NEW YORK

                                    by  /s/ Mary Beth Lewicki
                                        ----------------------------------
                                        Name:  Mary Beth Lewicki
                                        Title: Vice President



<PAGE>   1
                                                                     EXHIBIT 4.2


                                                                  EXECUTION COPY

                               Up to $200,000,000

                           Human Genome Sciences, Inc.

             5% Convertible Subordinated Notes due December 15, 2006

                          REGISTRATION RIGHTS AGREEMENT

                                                               December 14, 1999

Credit Suisse First Boston Corporation
Eleven Madison Avenue
New York, New York  10010-3629

Dear Sirs:

               Human Genome Sciences, Inc., a Delaware corporation (the
"Company"), proposes to issue and sell to Credit Suisse First Boston Corporation
("CSFBC"), (the "Initial Purchaser"), upon the terms set forth in a purchase
agreement of even date herewith (the "Purchase Agreement"), $150,000,000
aggregate principal amount (plus up to an additional $50,000,000 principal
amount at the option of the Initial Purchaser) of 5% Convertible Subordinated
Notes Due December 15, 2006 (the "Notes") of the Company. The Notes will be
convertible into shares of Common Stock, par value $0.01 per share, of the
Company (the "Common Stock") at the conversion price set forth in the Offering
Circular dated December 8, 1999. The Notes will be issued pursuant to an
Indenture, dated as of December 14, 1999 (the "Indenture"), between the Company
and The Bank of New York (the "Trustee"). As an inducement to the Initial
Purchaser to enter into the Purchase Agreement and in satisfaction of a
condition to the Initial Purchaser's obligations thereunder, the Company agrees
with the Initial Purchaser, (i) for the benefit of the Initial Purchaser and
(ii) for the benefit of the holders of the Notes and the Common Stock issuable
upon conversion of the Notes (collectively, the "Securities") from time to time
until such time as such Securities have been sold pursuant to a Shelf
Registration Statement (as defined below) (each of the foregoing a "Holder" and
together the "Holders"), as follows:

               1.  Shelf Registration.  The Company shall take the following
actions:

               (a) The Company shall, at its cost, prepare and, as promptly as
practicable (but in no event more than 60 days after so required or requested
pursuant to this Section 1) file with the Securities and Exchange Commission
(the "Commission") and thereafter shall use its best efforts to cause to be
declared

<PAGE>   2

                                                                               2

effective as soon as practicable a registration statement on Form S-3 (the
"Shelf Registration Statement") covering the offer and sale of the Transfer
Restricted Securities (as defined in Section 5 hereof) by the Holders thereof
from time to time in accordance with the methods of distribution set forth in
the Shelf Registration Statement and Rule 415 under the Securities Act of 1933,
as amended (the "Securities Act") (hereinafter, the "Shelf Registration");
provided, however, that no Holder (other than the Initial Purchaser) shall be
entitled to have the Securities held by it covered by such Shelf Registration
Statement unless such Holder agrees in writing to be bound by all the provisions
of this Agreement applicable to such Holder.

               (b) The Company shall use its best efforts to keep the Shelf
Registration Statement continuously effective, in order to permit the prospectus
included therein to be lawfully delivered by the Holders of the relevant
Securities, for a period of two years (or for such longer period if extended
pursuant to Section 2(h) below) from the date of its effectiveness or such
shorter period that will terminate when all the Securities covered by the Shelf
Registration Statement (i) have been sold pursuant thereto or (ii) may be sold
pursuant to Rule 144(k) under the Securities Act (or any successor rule
therefore), assuming for this purpose that the Holders thereof are not
affiliates of the Company (in any such case, such period being called the "Shelf
Registration Period"). The Company shall be deemed not to have used its best
efforts to keep the Shelf Registration Statement effective during the requisite
period if it voluntarily takes any action that would result in Holders of
Securities covered thereby not being able to offer and sell such Securities
during that period, unless (i) such action is required by applicable law or (ii)
upon the occurrence of any event contemplated by paragraph 2(b)(v) below, such
action is taken by the Company in good faith and for valid business reasons and
the Company thereafter complies with the requirements of paragraph 2(h).

               (c) Notwithstanding any other provisions of this Agreement to the
contrary, the Company shall cause the Shelf Registration Statement and the
related prospectus and any amendment or supplement thereto, as of the effective
date of the Shelf Registration Statement, amendment or supplement, (i) to comply
in all material respects with the applicable requirements of the Securities Act
and the rules and regulations of the Commission and (ii) not to contain any
untrue statement of a material fact or omit to state a material fact required to
be stated therein or necessary to make the statements therein, in light of the
circumstances under which they were made, not misleading.


<PAGE>   3
                                                                               3

               2. Registration Procedures. In connection with the Shelf
Registration contemplated by Section 1 hereof the following provisions shall
apply:

               (a) The Company shall (i) furnish to the Initial Purchaser, prior
to the filing thereof with the Commission, a copy of the Shelf Registration
Statement and each amendment thereof and each amendment or supplement, if any,
to the prospectus included therein and, in the event that an Initial Purchaser
(with respect to any portion of an unsold allotment from the original offering)
is participating in the Shelf Registration Statement, shall use its best efforts
to reflect in each such document, when so filed with the Commission, such
comments as the Initial Purchaser reasonably may propose; and (ii) include the
names of the Holders who propose to sell Securities pursuant to the Shelf
Registration Statement, as selling security holders.

               (b) The Company shall give written notice to the Initial
Purchaser and the Holders (which notice pursuant to clauses (ii)-(v) hereof
shall be accompanied by an instruction to suspend the use of the prospectus
until the requisite changes have been made):

               (i) when the Shelf Registration Statement or any amendment
        thereto has been filed with the Commission and when the Shelf
        Registration Statement or any post-effective amendment thereto has
        become effective;

               (ii) of any request by the Commission for amendments or
        supplements to the Shelf Registration Statement or the prospectus
        included therein or for additional information;

               (iii) of the issuance by the Commission of any stop order
        suspending the effectiveness of the Shelf Registration Statement or the
        initiation of any proceedings for that purpose;

               (iv) of the receipt by the Company or its legal counsel of any
        notification with respect to the suspension of the qualification of the
        Securities for sale in any jurisdiction or the initiation or threatening
        of any proceeding for such purpose; and

               (v) of the happening of any event or circumstance that would
        require the Company to make changes in the Shelf Registration Statement
        or the prospectus in order that the Shelf Registration Statement or the
        prospectus do not contain an untrue statement of a material fact nor
        omit to state a material fact required to be stated therein or necessary
        to make the statements therein (in the case of the

<PAGE>   4
                                                                               4


        prospectus, in light of the circumstances under which they were made)
        not misleading, which written notice need not provide any detail as to
        the nature of such event.

               (c) The Company shall make every reasonable effort to obtain the
withdrawal, at the earliest possible time, of any order suspending the
effectiveness of the Shelf Registration Statement.

               (d) The Company shall furnish to each Holder of Securities
included within the coverage of the Shelf Registration, without charge, at least
one copy of the Shelf Registration Statement and any post-effective amendment
thereto, including financial statements and schedules, and, if the Holder so
requests in writing, all exhibits thereto (including those, if any, incorporated
by reference).

               (e) The Company shall, during the Shelf Registration Period,
deliver to each Holder of Securities included within the coverage of the Shelf
Registration Statement, without charge, as many copies of the prospectus
(including each preliminary prospectus) included in the Shelf Registration
Statement and any amendment or supplement thereto as such person may reasonably
request. The Company consents, subject to the provisions of this Agreement, to
the use of the prospectus or any amendment or supplement thereto by each of the
selling Holders in connection with the offering and sale of the Securities
covered by the prospectus, or any amendment or supplement thereto, included in
the Shelf Registration Statement.

               (f) Prior to any public offering of the Securities, pursuant to
the Shelf Registration Statement, the Company shall register or qualify or
cooperate with the Holders of the Securities included therein and their
respective counsel in connection with the registration or qualification of such
Securities for offer and sale under the securities or "blue sky" laws of such
states of the United States as any such Holder reasonably requests in writing
and do any and all other acts or things necessary or advisable to enable the
offer and sale in such jurisdictions of the Securities covered by the Shelf
Registration Statement; provided, however, that the Company shall not be
required to (i) qualify generally to do business in any jurisdiction where it is
not then so qualified or (ii) take any action which would subject it to general
service of process or to taxation in any jurisdiction where it is not then so
subject.

               (g) The Company shall cooperate with the Holders of the
Securities to facilitate the timely preparation and delivery of certificates
representing the Securities to be sold pursuant to the Shelf Registration
Statement free of any restrictive legends and in such denominations and
registered in such names as

<PAGE>   5
                                                                               5


the Holders may request a reasonable period of time prior to sales of the
Securities pursuant to the Shelf Registration Statement.

               (h) Upon the occurrence of any event contemplated by paragraphs
(ii) through (v) of Section 2(b) above during the period for which the Company
is required to maintain an effective Shelf Registration Statement, the Company
shall, as required hereby, prepare and file a post-effective amendment to the
Shelf Registration Statement or an amendment or supplement to the related
prospectus and any other required document so that, as thereafter delivered to
Holders or purchasers of Securities, the prospectus will not contain an untrue
statement of a material fact or omit to state any material fact required to be
stated therein or necessary to make the statements therein, in light of the
circumstances under which they were made, not misleading. If the Company
notifies the Initial Purchaser and the Holders in accordance with paragraphs
(ii) through (v) of Section 2(b) above to suspend the use of the prospectus
until the requisite changes to the prospectus have been made, then the Initial
Purchaser and the Holders shall suspend use of such prospectus and the period of
effectiveness of the Shelf Registration Statement provided for in Section 1(b)
above shall be extended by the number of days from and including the date of
giving such notice to and including the date when the Initial Purchaser and the
Holders shall have received such amended or supplemented prospectus pursuant to
this Section 2(h). Any such amendment, supplement or document will be prepared
and filed as promptly as practicable under the circumstances, as determined in
good faith by the Company, it being understood that the Company may have bona
fide reasons to delay such preparation and filing for a period which may not in
any event exceed 60 days.

               (i) Not later than the effective date of the Shelf Registration
Statement, the Company will provide CUSIP numbers for the Notes and the Common
Stock registered under the Shelf Registration Statement, and provide the Trustee
with printed certificates for such Notes, in form eligible for deposit with The
Depository Trust Company.

               (j) The Company will comply with all rules and regulations of the
Commission to the extent and so long as they are applicable to the Shelf
Registration and will make generally available to its security holders (or
otherwise provide in accordance with Section 11(a) of the Securities Act) an
earnings statement satisfying the provisions of Section 11(a) of the Securities
Act, no later than 45 days after the end of a 12-month period (or 90 days, if
such period is a fiscal year) beginning with the first month of the Company's
first fiscal quarter commencing after the effective date of the Shelf
Registration Statement, which statement shall cover such 12-month period.


<PAGE>   6

                                                                               6



               (k) The Company shall cause the Indenture to be qualified under
the Trust Indenture Act of 1939, as amended (the "Trust Indenture Act"), in a
timely manner and containing such changes, if any, as shall be necessary for
such qualification. In the event that such qualification would require the
appointment of a new trustee under the Indenture, the Company shall appoint a
new trustee thereunder pursuant to the applicable provisions of the Indenture.

               (l) The Company may require each Holder of Securities to be sold
pursuant to the Shelf Registration Statement to furnish to the Company such
information regarding the Holder and the distribution of the Securities as the
Company may from time to time reasonably require for inclusion in the Shelf
Registration Statement, and the Company may exclude from such registration the
Securities of any Holder that fails to furnish such information within a
reasonable time after receiving such request.

               (m) The Company shall enter into such customary agreements
(including, if requested, an underwriting agreement in customary form) and take
all other actions, if any, as any Holder shall reasonably request in order to
facilitate the disposition of the Securities pursuant to the Shelf Registration,
provided, however, that the Company shall not be required to facilitate an
underwritten offering pursuant to the Shelf Registration Statement by any
Holders unless the offering relates to at least $50,000,000 principal amount of
the Notes or the equivalent number of shares of Common Stock into which such
Notes are convertible.

               (n) The Company shall (i) make reasonably available for
inspection by the Holders of the Securities, any underwriter participating in
any distribution pursuant to the Shelf Registration Statement and any attorney,
accountant or other agent retained by the Holders of the Securities or any such
underwriter all relevant financial and other records, pertinent corporate
documents and properties of the Company and (ii) cause the Company's officers,
directors, employees, accountants and auditors to supply all relevant
information reasonably requested by the Holders of the Securities or any such
underwriter, attorney, accountant or agent in connection with the Shelf
Registration Statement, in each case, as shall be reasonably necessary to enable
such persons, to conduct a reasonable investigation within the meaning of
Section 11 of the Securities Act; provided, however, that the foregoing
inspection and information gathering (i) shall be coordinated on behalf of the
Initial Purchaser by you and on behalf of the other parties, by one counsel
designated by and on behalf of the other parties as described in Section 3
hereof.




<PAGE>   7
                                                                               7



               (o) The Company, if requested by any Holder of Securities covered
by Shelf Registration Statement, shall cause (i) its counsel (which may include
the Company's general counsel for one or more of the opinions) to deliver an
opinion and updates thereof relating to the Securities in customary form
addressed to such Holders, and the managing underwriters, if any, thereof, and
dated, in the case of the initial opinion, the effective date of such Shelf
Registration Statement (it being agreed that the matters to be covered by such
opinion shall include, without limitation, the due incorporation and good
standing of the Company; the qualification of the Company to transact business
as a foreign corporation; the due authorization, execution and delivery of the
relevant agreement of the type referred to in Section 2(m) hereof; the due
authorization, execution, authentication and issuance, and the validity and
enforceability, of the applicable Securities; the absence of material legal or
governmental proceedings involving the Company; the absence of governmental
approvals required to be obtained in connection with the Shelf Registration
Statement, the offering and sale of the applicable Securities, or any agreement
of the type referred to in Section 2(m) hereof; the compliance as to form of
such Shelf Registration Statement and any documents incorporated by reference
therein and of the Indenture with the requirements of the Securities Act and the
Trust Indenture Act, respectively; and, as of the date of the opinion and as of
the effective date of the Shelf Registration Statement or most recent
post-effective amendment thereto, as the case may be, the absence from such
Shelf Registration Statement and the prospectus included therein, as then
amended or supplemented, and from any documents incorporated by reference
therein of an untrue statement of a material fact or the omission to state
therein a material fact required to be stated therein or necessary to make the
statements therein not misleading (in the case of any such documents, in the
light of the circumstances existing at the time that such documents were filed
with the Commission under the Securities Exchange Act of 1934, as amended (the
"Exchange Act")), (ii) its officers to execute and deliver all customary
documents and certificates and updates thereof requested by any underwriters of
the applicable Securities or counsel for the Holders and (iii) its independent
public accountants and the independent public accountants with respect to any
other entity for which financial information is provided in the Shelf
Registration Statement to provide to the selling Holders of the applicable
Securities and any underwriter therefor a comfort letter in customary form and
covering matters of the type customarily covered in comfort letters in
connection with primary underwritten offerings, subject to receipt of
appropriate documentation as contemplated, and only if permitted, by Statement
of Auditing Standards No. 72.


<PAGE>   8
                                                                               8


               (p) The Company shall use its best efforts to take all other
steps necessary to effect the registration of the Securities covered by the
Shelf Registration Statement contemplated hereby.

               3. Registration Expenses. The Company shall bear all fees and
expenses incurred in connection with the performance of its obligations under
Sections 1 through 2 hereof (including the reasonable fees and expenses, if any,
of Cravath, Swaine & Moore, counsel for the Initial Purchaser, incurred in
connection with the Shelf Registration), whether or not the Shelf Registration
Statement is filed or becomes effective, and shall bear or reimburse the Holders
of the Securities covered by the Shelf Registration for the reasonable fees and
disbursements of one firm of counsel designated by the Holders of a majority in
principal amount of the Securities covered by the Shelf Registration Statement
(provided that Holders of Common Stock issued upon the conversion of the Notes
shall be deemed to be Holders of the aggregate principal amount of Notes from
which such Common Stock was converted) to act as counsel for the Holders in
connection therewith.

               4. Indemnification. (a) The Company agrees to indemnify and hold
harmless each Holder and each person, if any, who controls such Holder within
the meaning of the Securities Act or the Exchange Act (each Holder and such
controlling persons are referred to collectively as the "Indemnified Parties")
from and against any losses, claims, damages or liabilities, joint or several,
or any actions in respect thereof (including, but not limited to, any losses,
claims, damages, liabilities or actions relating to purchases and sales of the
Securities) to which each Indemnified Party becomes subject under the Securities
Act, the Exchange Act or otherwise, insofar as such losses, claims, damages,
liabilities or actions arise out of or are based upon any untrue statement or
alleged untrue statement of a material fact contained in the Shelf Registration
Statement or prospectus, including any document incorporated by reference
therein, or in any amendment or supplement thereto or in any preliminary
prospectus relating to the Shelf Registration, or arise out of, or are based
upon, the omission or alleged omission to state therein a material fact required
to be stated therein or necessary to make the statements therein not misleading,
and shall reimburse, as incurred, the Indemnified Parties for any legal or other
expenses reasonably incurred by them in connection with investigating or
defending any such loss, claim, damage, liability or action in respect thereof;
provided, however, that (i) the Company shall not be liable in any such case to
the extent that such loss, claim, damage or liability arises out of or is based
upon any untrue statement or alleged untrue statement or omission or alleged
omission made in the Shelf Registration Statement or prospectus or in any
amendment or supplement thereto

<PAGE>   9

                                                                               9



or in any preliminary prospectus relating to the Shelf Registration in reliance
upon and in conformity with written information pertaining to such Holder and
furnished to the Company by or on behalf of such Holder specifically for
inclusion therein and (ii) with respect to any untrue statement or omission or
alleged untrue statement or omission made in any preliminary prospectus relating
to the Shelf Registration Statement, the indemnity agreement contained in this
subsection (a) shall not inure to the benefit of any Holder from whom the person
asserting any such losses, claims, damages or liabilities purchased the
Securities concerned, to the extent that a prospectus relating to such
Securities was required to be delivered by such Holder under the Securities Act
in connection with such purchase and any such loss, claim, damage or liability
of such Holder results from the fact that there was not sent or given to such
person, at or prior to the written confirmation of the sale of such Securities
to such person, a copy of the final prospectus if the Company had previously
furnished copies thereof to such Holder; provided further, however, that this
indemnity agreement will be in addition to any liability which the Company may
otherwise have to such Indemnified Party.

               The Company shall also indemnify the underwriters, their officers
and directors and each person who controls such underwriters within the meaning
of the Securities Act or the Exchange Act to the same extent as provided above
with respect to the indemnification of the Holders if requested by such Holders.

               (b) Each Holder, severally and not jointly, will indemnify and
hold harmless the Company, its officers and directors and each person, if any,
who controls the Company within the meaning of the Securities Act or the
Exchange Act from and against any losses, claims, damages or liabilities or any
actions in respect thereof, to which the Company or any such controlling person
may become subject under the Securities Act, the Exchange Act or otherwise,
insofar as such losses, claims, damages, liabilities or actions arise out of or
are based upon any untrue statement or alleged untrue statement of a material
fact contained in a Shelf Registration Statement or prospectus or in any
amendment or supplement thereto or in any preliminary prospectus relating to a
Shelf Registration, or arise out of or are based upon the omission or alleged
omission to state therein a material fact necessary to make the statements
therein not misleading, but in each case only to the extent that the untrue
statement or omission or alleged untrue statement or omission was made in
reliance upon and in conformity with written information pertaining to such
Holder and furnished to the Company by or on behalf of such Holder specifically
for inclusion therein; and, subject to the limitation set forth immediately
preceding this clause, shall reimburse, as incurred, the Company for any legal
or other expenses reasonably incurred by the Company or any such

<PAGE>   10

                                                                              10



controlling person in connection with investigating or defending any loss,
claim, damage, liability or action in respect thereof. This indemnity agreement
will be in addition to any liability which such Holder may otherwise have to the
Company or any of its controlling persons.

               (c) Promptly after receipt by an indemnified party under this
Section 4 of notice of the commencement of any action or proceeding (including a
governmental investigation), such indemnified party will, if a claim in respect
thereof is to be made against the indemnifying party under this Section 4,
notify the indemnifying party of the commencement thereof; but the omission so
to notify the indemnifying party will not, in any event, relieve the
indemnifying party from any obligations to any indemnified party other than the
indemnification obligation provided in subsections (a) or (b) above. In case any
such action is brought against any indemnified party, and it notifies the
indemnifying party of the commencement thereof, the indemnifying party will be
entitled to participate therein and, to the extent that it may wish, jointly
with any other indemnifying party similarly notified, to assume the defense
thereof, with counsel reasonably satisfactory to such indemnified party (who
shall not, except with the consent of the indemnified party, be counsel to the
indemnifying party), and after notice from the indemnifying party to such
indemnified party of its election so to assume the defense thereof the
indemnifying party will not be liable to such indemnified party under this
Section 4 for any legal or other expenses, other than reasonable costs of
investigation, subsequently incurred by such indemnified party in connection
with the defense thereof. No indemnifying party shall, without the prior written
consent of the indemnified party, effect any settlement of any pending or
threatened action in respect of which any indemnified party is or could have
been a party and indemnity could have been sought hereunder by such indemnified
party unless such settlement includes an unconditional release of such
indemnified party from all liability on any claims that are the subject matter
of such action.

               (d) If the indemnification provided for in this Section 4 is
unavailable or insufficient to hold harmless an indemnified party under
subsections (a) or (b) above, then each indemnifying party shall contribute to
the amount paid or payable by such indemnified party as a result of the losses,
claims, damages or liabilities (or actions in respect thereof) referred to in
subsections (a) or (b) above (i) in such proportion as is appropriate to reflect
the relative benefits received by the indemnifying party or parties on the one
hand and the indemnified party on the other from the registration of the
Securities, pursuant to the Shelf Registration, or (ii) if the allocation
provided by the foregoing clause (i) is not permitted by


<PAGE>   11


                                                                              11




applicable law, in such proportion as is appropriate to reflect not only the
relative benefits referred to in clause (i) above but also the relative fault of
the indemnifying party or parties on the one hand and the indemnified party on
the other in connection with the statements or omissions that resulted in such
losses, claims, damages or liabilities (or actions in respect thereof) as well
as any other relevant equitable considerations. The relative fault of the
parties shall be determined by reference to, among other things, whether the
untrue or alleged untrue statement of a material fact or the omission or alleged
omission to state a material fact relates to information supplied by the Company
on the one hand or such Holder or such other indemnified party, as the case may
be, on the other, and the parties' relative intent, knowledge, access to
information and opportunity to correct or prevent such statement or omission.
The amount paid by an indemnified party as a result of the losses, claims,
damages or liabilities referred to in the first sentence of this subsection (d)
shall be deemed to include any legal or other expenses reasonably incurred by
such indemnified party in connection with investigating or defending any action
or claim which is the subject of this subsection (d). Notwithstanding any other
provision of this Section 4(d), the Holders shall not be required to contribute
any amount in excess of the amount by which the net proceeds received by such
Holders from the sale of the Securities pursuant to the Shelf Registration
Statement exceeds the amount of damages which such Holders have otherwise been
required to pay by reason of such untrue or alleged untrue statement or omission
or alleged omission. No person guilty of fraudulent misrepresentation (within
the meaning of Section 11(f) of the Securities Act) shall be entitled to
contribution from any person who was not guilty of such fraudulent
misrepresentation. For purposes of this paragraph (d), each person, if any, who
controls such indemnified party within the meaning of the Securities Act or the
Exchange Act shall have the same rights to contribution as such indemnified
party and each person, if any, who controls the Company within the meaning of
the Securities Act or the Exchange Act shall have the same rights to
contribution as the Company.

               (e) The agreements contained in this Section 4 shall survive the
sale of the Securities pursuant to the Shelf Registration Statement and shall
remain in full force and effect, regardless of any termination or cancellation
of this Agreement or any investigation made by or on behalf of any indemnified
party.

               5. Additional Interest Under Certain Circumstances. (a)
Additional interest (the "Additional Interest") with respect to the Notes shall
be assessed as follows if any of the following events occur (each such event in
clauses (i) through (iii) below being herein called a "Registration Default"):


<PAGE>   12


                                                                              12



               (i) if on or prior to the 60th day after the first date of
        original issuance of the Notes, the Shelf Registration Statement has not
        been filed with the Commission;

               (ii) if on or prior to the 120th day after the first date of
        original issuance of the Notes, the Shelf Registration Statement has not
        been declared effective by the Commission; or

               (iii) if after the Shelf Registration Statement is declared
        effective (A) the Shelf Registration Statement thereafter ceases to be
        effective; or (B) the Shelf Registration Statement or the related
        prospectus ceases to be usable in connection with resales of Transfer
        Restricted Securities (as defined below) during the periods specified
        herein because either (1) any event occurs as a result of which the
        related prospectus forming part of such Shelf Registration Statement
        would include any untrue statement of a material fact or omit to state
        any material fact necessary to make the statements therein in the light
        of the circumstances under which they were made not misleading, or (2)
        it shall be necessary to amend such Shelf Registration Statement or
        supplement the related prospectus, to comply with the Securities Act or
        the Exchange Act or the respective rules thereunder.

               Additional Interest shall accrue on the Notes over and above the
interest set forth in the title of the Notes from and including the date on
which any such Registration Default shall occur, to but excluding the date on
which all such Registration Defaults have been cured, at a rate of 0.50% per
annum.

               (b) A Registration Default referred to in Section 5(a)(iii)(B)
shall be deemed not to have occurred and be continuing in relation to the Shelf
Registration Statement or the related prospectus if (i) such Registration
Default has occurred solely as a result of (x) the filing of a post-effective
amendment to the Shelf Registration Statement to incorporate annual audited
financial information with respect to the Company where such post-effective
amendment is not yet effective and needs to be declared effective to permit
Holders to use the related prospectus or (y) other material events, with respect
to the Company that would need to be described in the Shelf Registration
Statement or the related prospectus and (ii) in the case of clause (y), the
Company is proceeding in good faith to amend or supplement the Shelf
Registration Statement and related prospectus to describe such events as
required by paragraph 2(h) hereof; provided, however, that in any case if such
Registration Default occurs for a continuous period in excess of 60 days,
Additional Interest shall be payable in accordance with the above

<PAGE>   13

                                                                              13



paragraph from the day such Registration Default occurs until such Registration
Default is cured.

               (c) Any amounts of Additional Interest due pursuant to clause
(a)(i), (a)(ii) or (a)(iii) of this Section 5 will be payable in cash on the
regular interest payment dates with respect to the Notes. The amount of
Additional Interest will be determined by multiplying the applicable Additional
Interest rate by the principal amount of the Notes, multiplied by a fraction,
the numerator of which is the number of days such Additional Interest rate was
applicable during such period (determined on the basis of a 360-day year
comprised of twelve 30-day months), and the denominator of which is 360. The
indebtedness represented by the Additional Interest shall be subordinated in
right of payment to all existing and future Senior Indebtedness (as defined in
the Indenture) as and to the same extent as the Notes.

               (d) "Transfer Restricted Securities" means each Security until
(i) the date on which such Security has been effectively registered under the
Securities Act and disposed of in accordance with the Shelf Registration
Statement or (ii) the date on which such Security is distributed to the public
pursuant to Rule 144 under the Securities Act or is saleable pursuant to Rule
144(k) under the Securities Act.

               6. Rules 144 and 144A. The Company shall use its best efforts to
file the reports required to be filed by it under the Securities Act and the
Exchange Act in a timely manner and, if at any time the Company is not required
to file such reports, it will, upon the request of any Holder, make publicly
available other information so long as necessary to permit sales of their
securities pursuant to Rules 144 and 144A. The Company covenants that it will
take such further action as any Holder of Securities may reasonably request, all
to the extent required from time to time to enable such Holder to sell Transfer
Restricted Securities without registration under the Securities Act within the
limitations of the exemptions provided by Rules 144 and 144A (including the
requirements of Rule 144A(d)(4)). The Company will provide a copy of this
Agreement to prospective purchasers of Securities identified to the Company by
the Initial Purchaser upon request. Upon the request of any Holder, the Company
shall deliver to such Holder a written statement as to whether it has complied
with such requirements. Notwithstanding the foregoing, nothing in this Section 6
shall be deemed to require the Company to register any of its securities
pursuant to the Exchange Act.

               7. Underwritten Registrations. If any of the Transfer Restricted
Securities covered by the Shelf Registration are to be sold in an underwritten
offering, the investment banker or investment bankers and manager or managers
that will administer


<PAGE>   14


                                                                              14




the offering ("Managing Underwriters") will be selected by the Holders of a
majority in aggregate principal amount of such Transfer Restricted Securities to
be included in such offering (provided that Holders of Common Stock issued upon
conversion of Notes shall not be deemed Holders of Common Stock, but shall be
deemed to be Holders of the aggregate principal amount of Notes from which such
Common Stock was converted).

               No person may participate in any underwritten registration
hereunder unless such person (i) agrees to sell such person's Transfer
Restricted Securities on the basis reasonably provided in any underwriting
arrangements approved by the persons entitled hereunder to approve such
arrangements and (ii) completes and executes all questionnaires, powers of
attorney, indemnities, underwriting agreements and other documents reasonably
required under the terms of such underwriting arrangements.

               8. Miscellaneous. (a) Amendments and Waivers. The provisions of
this Agreement may not be amended, modified or supplemented, and waivers or
consents to departures from the provisions hereof may not be given, except by
the Company and the written consent of the Holders of a majority in principal
amount of the Securities (provided that Holders of Common Stock issued upon
conversion of Notes shall not be deemed Holders of Common Stock, but shall be
deemed to be Holders of the aggregate principal amount of Notes from which such
Common Stock was converted) affected by such amendment, modification,
supplement, waiver or consents.

               (b) Notices. All notices and other communications provided for or
permitted hereunder shall be made in writing by hand delivery, first-class mail,
facsimile transmission, or air courier which guarantees overnight delivery:

               (1) if to a Holder, at the most current address given by such
        Holder to the Company;

               (2) if to the Initial Purchaser, at its address as follows:

                    Credit Suisse First Boston Corporation
                    Eleven Madison Avenue
                    New York, NY 10010-3629
                    Fax No.:  (212) 325-8278
                    Attention:  Transactions Advisory Group


<PAGE>   15

                                                                              15


        with a copy to:

                      Cravath, Swaine & Moore
                      Worldwide Plaza
                      825 Eighth Avenue
                      New York, NY 10019
                      Fax No.:  (212) 474-3700
                      Attention:  Robert Rosenman, Esq.

               (3) if to the Company, at its address as follows:

                      Human Genome Sciences, Inc.
                      9410 Key West Avenue
                      Rockville, MD 20850
                      Fax No.:  (301) 309-8439
                      Attention:  James H. Davis, Esq.

        with a copy to:

                      Piper Marbury Rudnick & Wolfe LLP
                      36 South Charles Street
                      Baltimore, Maryland 21201
                      Fax No.:  (410) 539-0489
                      Attention:  R. W. Smith, Jr., Esq.

               All such notices and communications shall be deemed to have been
duly given: at the time delivered by hand, if personally delivered; three
business days after being deposited in the mail, postage prepaid, if mailed;
when receipt is acknowledged by recipient's facsimile machine operator, if sent
by facsimile transmission; and on the day delivered, if sent by overnight air
courier guaranteeing next day delivery.

               (c) No Inconsistent Agreements. The Company has not, as of the
date hereof, entered into, nor shall it, on or after the date hereof, without
the prior consent of CSFBC, enter into, any agreement with respect to its
securities that is inconsistent with the rights granted to the Holders herein or
otherwise conflicts with the provisions hereof.

               (d) Successors and Assigns. This Agreement shall be binding upon
the Company and its successors and assigns.

               (e) Counterparts. This Agreement may be executed in any number of
counterparts and by the parties hereto in separate counterparts, each of which
when so executed shall be deemed to be an original and all of which taken
together shall constitute one and the same agreement.


<PAGE>   16

                                                                              16


               (f) Headings. The headings in this Agreement are for convenience
of reference only and shall not limit or otherwise affect the meaning hereof.

               (g) Governing Law. THIS AGREEMENT SHALL BE GOVERNED BY, AND
CONSTRUED IN ACCORDANCE WITH, THE LAWS OF THE STATE OF NEW YORK WITHOUT REGARD
TO PRINCIPLES OF CONFLICTS OF LAWS.

               By the execution and delivery of this Agreement, the Company
submits to the nonexclusive jurisdiction of any federal or state court in the
State of New York.

               (h) Severability. If any one or more of the provisions contained
herein, or the application thereof in any circumstance, is held invalid, illegal
or unenforceable, the validity, legality and enforceability of any such
provision in every other respect and of the remaining provisions contained
herein shall not be affected or impaired thereby.

               (i) Securities Held by the Company. Whenever the consent or
approval of Holders of a specified percentage of principal amount of Securities
is required hereunder, Securities held by the Company or its affiliates (other
than subsequent Holders of Securities if such subsequent Holders are deemed to
be affiliates solely by reason of their holdings of such Securities)shall not be
counted in determining whether such consent or approval was given by the Holders
of such required percentage.


<PAGE>   17




               If the foregoing is in accordance with your understanding of our
agreement, please sign and return to the Company a counterpart hereof, whereupon
this instrument, along with all counterparts, will become a binding agreement
among the Initial Purchaser and the Company in accordance with its terms.

                                                   Very truly yours,

                                                   HUMAN GENOME SCIENCES, INC.

                                                   By: /s/   Steven C. Mayer
                                                      --------------------------
                                                      Name:  Steven C. Mayer
                                                      Title: Senior Vice
                                                             President and Chief
                                                             Financial Officer

The foregoing Registration
Rights Agreement is hereby confirmed
and accepted as of the date first
above written.

CREDIT SUISSE FIRST BOSTON CORPORATION

By:  /s/  Russell T. Ray
   ------------------------------
   Name:  Russell T. Ray
   Title: Managing Director



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