RIBOGENE INC / CA/
8-K, 1999-07-15
COMMERCIAL PHYSICAL & BIOLOGICAL RESEARCH
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<PAGE>   1

                       SECURITIES AND EXCHANGE COMMISSION
                             WASHINGTON, D. C. 20549

                                    FORM 8-K

                      RELATING TO ADOPTION OF A RIGHTS PLAN


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


         Date of Report (Date of earliest event reported): July 1, 1999


                                 RIBOGENE, INC.
             (Exact name of registrant as specified in its charter)


                                    DELAWARE
                 (State or other jurisdiction of incorporation)


      001-14165                                           94-3095154
(Commission File No.)                          (IRS Employer Identification No.)


                               26118 RESEARCH ROAD
                                HAYWARD, CA 94545
              (Address of principal executive offices and zip code)


       Registrant's telephone number, including area code: (510) 732-5551


<PAGE>   2


ITEM 5.    OTHER EVENTS.

         On July 1, 1999 the Board of Directors of RIBOGENE, INC. (the
"Company") approved the adoption of a Share Purchase Rights Plan (the "Plan").
Terms of the Plan provide for a dividend distribution of one preferred share
purchase right (a "Right") for each outstanding share of common stock, par value
$.001 per share (the "Common Shares"), of the Company. The dividend is payable
on July 23, 1999 (the "Record Date") to the stockholders of record on that date.
Each Right entitles the registered holder to purchase from the Company one
one-hundredth of a share of Series B Junior Participating Preferred Stock, par
value $.001 per share (the "Preferred Shares"), at a price of $25.00 per one
one-hundredth of a Preferred Share (the "Purchase Price"), subject to
adjustment. Each one one-hundredth of a share of Preferred Shares has
designations and powers, preferences and rights, and the qualifications,
limitations and restrictions which make its value approximately equal to the
value of a Common Share. The description and terms of the Rights are set forth
in a Rights Agreement (the "Rights Agreement"), dated as of July 1, 1999 entered
into between the Company and American Stock Transfer, as rights agent (the
"Rights Agent").

         Initially, the Rights will be evidenced by the stock certificates
representing the Common Shares then outstanding, and no separate Right
Certificates, as defined, will be distributed. Until the earlier to occur of (i)
the date of a public announcement that a person, entity or group of affiliated
or associated persons have acquired beneficial ownership of 20% or more of the
outstanding Common Shares (an "Acquiring Person") or (ii) 10 business days (or
such later date as may be determined by action of the Board of Directors prior
to such time as any person or entity becomes an Acquiring Person) following the
commencement of, or announcement of an intention to commence, a tender offer or
exchange offer the consummation of which would result in any person or entity
becoming an Acquiring Person (the earlier of such dates being called the
"Distribution Date"), the Rights will be evidenced, with respect to any of the
Common Share certificates outstanding as of the Record Date, by such Common
Share certificate with or without a copy of the Summary of Rights, which is
included in the Rights Agreement as Exhibit C thereof (the "Summary of Rights").

         Until the Distribution Date, the Rights will be transferable with and
only with the Common Shares. Until the Distribution Date (or earlier redemption
or expiration of the Rights), new Common Share certificates issued after the
Record Date, upon transfer or new issuance of Common Shares, will contain a
notation incorporating the Rights Agreement by reference. Until the Distribution
Date (or earlier redemption or expiration of the Rights), the surrender or
transfer of any certificates for Common Shares outstanding as of the Record
Date, even without such notation or a copy of the Summary of Rights being
attached thereto, will also constitute the transfer of the Rights associated
with the Common Shares represented by such certificate. As soon as practicable
following the Distribution Date, separate certificates evidencing the Rights
("Right Certificates") will be mailed to holders of record of the Common Shares
as of the close of business on the Distribution Date and such separate Right
Certificates alone will evidence the Rights.




                                       1.
<PAGE>   3

         The Rights are not exercisable until the Distribution Date. The Rights
will expire on June 30, 2009 (the "Final Expiration Date"), unless the Rights
are earlier redeemed or exchanged by the Company, in each case, as described
below.

         The Purchase Price payable, and the number of Preferred Shares or other
securities or other property, upon exercise of the Rights are subject to
adjustment from time to time to prevent dilution (i) in the event of a stock
dividend on, or a subdivision, combination or reclassification of, the Preferred
Shares, (ii) upon the grant to holders of the Preferred Shares of certain rights
or warrants to subscribe for or purchase Preferred Shares at a price, or
securities convertible into Preferred Shares with a conversion price, less than
the then current market price of the Preferred Shares or (iii) upon the
distribution to holders of the Preferred Shares of evidences of indebtedness or
assets (excluding regular periodic cash dividends paid out of earnings or
retained earnings or dividends payable in Preferred Shares) or of subscription
rights or warrants (other than those referred to above). The exercise of Rights
for Preferred Shares is at all times subject to the availability of a sufficient
number of authorized but unissued Preferred Shares.

         The number of outstanding Rights and the number of one one-hundredths
of a Preferred Share issuable upon exercise of each Right are also subject to
adjustment in the event of a stock split of the Common Shares or a stock
dividend on the Common Shares payable in Common Shares or subdivisions,
consolidation or combinations of the Common Shares occurring, in any case, prior
to the Distribution Date.

         Preferred Shares purchasable upon exercise of the Rights will not be
redeemable. Each Preferred Share will be entitled to a minimum preferential
quarterly dividend payment of $1.00 but will be entitled to an aggregate
dividend of 100 times the dividend declared per Common Share. In the event of
liquidation, the holders of the Preferred Shares would be entitled to a minimum
preferential liquidation payment of $100 per share, but would be entitled to
receive an aggregate payment equal to 100 times the payment made per Common
Share. Each Preferred Share will have 100 votes, voting together with the Common
Shares. Finally, in the event of any merger, consolidation or other transaction
in which Common Shares are exchanged, each Preferred Share will be entitled to
receive 100 times the amount of consideration received per Common Share. These
rights are protected by customary anti-dilution provisions. Because of the
nature of the Preferred Shares' dividend and liquidation rights, the value of
one one-hundredth of a Preferred Share should approximate the value of one
Common Share. The Preferred Shares would rank junior to any other series of the
Company's preferred stock.

         In the event that any person or group of affiliated or associated
persons becomes an Acquiring Person, proper provision shall be made so that each
holder of a Right, other than Rights beneficially owned by the Acquiring Person
and its associates and affiliates (which will thereafter be void), will for a
60-day period have the right to receive upon exercise that number of Common
Shares having a market value of two times the exercise price of the Right (or,
if such number of shares is not and cannot be authorized, the Company may issue
Preferred Shares, cash, debt, stock or a combination thereof in exchange for the
Rights). This right will terminate 60 days after the date on which the Rights
become nonredeemable (as described below), unless there is an injunction or
similar obstacle to exercise of the Rights, in which event this right will
terminate 60 days after the date on which the Rights again become exercisable.




                                       2.
<PAGE>   4

         Generally, under the Plan, an "Acquiring Person" shall not be deemed to
include (i) the Company, (ii) a subsidiary of the Company, (iii) any employee
benefit or compensation plan of the Company, (iv) any entity holding Common
Shares for or pursuant to the terms of any such employee benefit or compensation
plan or (v) an Excluded Person (as such term is hereinafter defined. In
addition, except under limited circumstances, no person or entity shall become
an Acquiring Person as the result of the acquisition of Common Shares by the
Company which, by reducing the number of shares outstanding, increases the
proportionate number of shares beneficially owned by such person or entity to
20% or more of the Common Shares then outstanding. Dr. Lindsay Rosenwald,
Paramount Capital Asset Management, Inc., the Aries Domestic Fund, L.P., The
Aries Trust and their associates and affiliates will be an Excluded Person so
long as they hold, in the aggregate, 22% or less of the Company's outstanding
common shares, as will Roberts Pharmaceutical Corporation.

         In the event that the Company is acquired in a merger or other business
combination transaction or 50% or more of its consolidated assets or earning
power are sold to an Acquiring Person, its associates or affiliates or certain
other persons in which such persons have an interest, proper provision will be
made so that each holder of a Right will thereafter have the right to receive,
upon the exercise thereof at the then current exercise price of the Right, that
number of shares of common stock of the acquiring company which at the time of
such transaction will have a market value of two times the exercise price of the
Right.

         At any time after an Acquiring Person becomes an Acquiring Person and
prior to the acquisition by such Acquiring Person of 50% or more of the
outstanding Common Shares, the Board of Directors of the Company may exchange
the Rights (other than Rights owned by such person or group which have become
void), in whole or in part, at an exchange ratio of one Common Share, or one
one-hundredth of a Preferred Share, per Right (or, at the election of the
Company, the Company may issue cash, debt, stock or a combination thereof in
exchange for the Rights), subject to adjustment.

         With certain exceptions, no adjustment in the Purchase Price will be
required until cumulative adjustments require an adjustment of at least 1% in
such Purchase Price. No fractional Preferred Shares will be issued (other than
fractions which are integral multiples of the number of one one-hundredths of a
Preferred Share issuable upon the exercise of one Right, which may, at the
election of the Company, be evidenced by depositary receipts), and in lieu
thereof, an adjustment in cash will be made based on the market price of the
Preferred Shares on the last trading day prior to the date of exercise.

         At any time prior to the earliest of (i) the day of the first public
announcement that a person has become an Acquiring Person or (ii) the Final
Expiration Date, the Board of Directors of the Company may redeem the Rights in
whole, but not in part, at a price of $.01 per Right (the "Redemption Price").
Following the expiration of the above periods, the Rights become nonredeemable.
Immediately upon any redemption of the Rights, the right to exercise the Rights
will terminate and the only right of the holders of Rights will be to receive
the Redemption Price.

         The terms of the Rights may be amended by the Board of Directors of the
Company without the consent of the holders of the Rights, except that from and
after such time as the




                                       3.
<PAGE>   5

rights are distributed no such amendment may adversely affect the interest of
the holders of the Rights excluding the interests of an Acquiring Person.

         Until a Right is exercised, the holder thereof, as such, will have no
rights as a stockholder of the Company, including, without limitation, the right
to vote or to receive dividends.

         The Rights have certain anti-takeover effects. The Rights will cause
substantial dilution to a person or group that attempts to acquire the Company
on terms not approved by the Company's Board of Directors. The Rights should not
interfere with any merger or other business combination approved by the Board of
Directors since the Rights may be amended to permit such acquisition or redeemed
by the Company at $.01 per Right prior to the earliest of (i) the time that a
person or group has acquired beneficial ownership of 20% or more of the Common
Shares or (ii) the final expiration date of the rights.

ITEM 7.    EXHIBITS.

<TABLE>
         <S>      <C>
         99.1     Press Release, dated as of July 13, 1999 entitled "RiboGene,
                  Inc. Adopts Stockholder Rights Plan."

         99.2     Rights Agreement dated as of July 1, 1999 among RiboGene, Inc.
                  and American Stock Transfer.

         99.3     Registrant's Certificate of Designation of Series B Junior
                  Participating Preferred Stock.

         99.4     Form of Rights Certificate.
</TABLE>




                                       4.
<PAGE>   6


                                    SIGNATURE

         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, thereunto duly authorized.


                                 RIBOGENE, INC.



Dated:  July 8, 1999             By: /s/ Timothy E. Morris
                                    -------------------------------
                                    TIMOTHY E. MORRIS
                                    Vice President, Finance and
                                    Administration, Chief Financial
                                    Officer and Assistant Secretary



                                       5.
<PAGE>   7


                                INDEX TO EXHIBITS


<TABLE>
         <S>      <C>
         99.1     Press Release, dated as of July 13, 1999 entitled "RiboGene,
                  Inc. Adopts Stockholder Rights Plan."

         99.2     Rights Agreement dated as of July 1, 1999 among RiboGene, Inc.
                  and American Stock Transfer.

         99.3     Registrant's Certificate of Designation of Series B Junior
                  Participating Preferred Stock

         99.4     Form of Rights Certificate.
</TABLE>



<PAGE>   1
                                                                   EXHIBIT  99.1


FOR IMMEDIATE RELEASE               CONTACT: CHARLES J. CASAMENTO
                                             CHAIRMAN, PRESIDENT & CEO
                                             TIMOTHY E. MORRIS
                                             VP FINANCE & ADMIN., CFO
                                             (510) 732-5551


                     RIBOGENE ADOPTS STOCKHOLDER RIGHTS PLAN

HAYWARD, CA, JULY 13, 1999 - RIBOGENE, INC. (AMEX:RBO) announced that its Board
of Directors approved the adoption of a Stockholder Rights Plan under which all
stockholders of record as of July 23, 1999 will receive rights to purchase
shares of a new series of Preferred Stock.

The Rights Plan is designed to enable all RiboGene stockholders to realize the
full value of their investment and to provide for fair and equal treatment for
all stockholders in the event that an unsolicited attempt is made to acquire
RiboGene. The adoption of the Rights Plan is intended as a means to guard
against abusive takeover tactics and is not in response to any particular
proposal.

The rights will be distributed as a non-taxable dividend and will expire in ten
years from the Record Date. The rights will be exercisable only if a person or
group acquires 20 percent or more of the RiboGene Common Stock or announces a
tender offer for 20 percent or more of the Common Stock. If a person acquires 20
percent or more of RiboGene's Common Stock, all rightsholders except the buyer
will be entitled to acquire RiboGene Common Stock at a discount. "Grandfathered"
stockholders and their affiliates and associates will be exempt from the Rights
Plan, unless "Grandfathered" stockholders acquire beneficial ownership of 22
percent or more of RiboGene's Common Stock. The effect will be to discourage
acquisitions of more than 20 percent of RiboGene's Common Stock without
negotiations with the RiboGene Board of Directors.

The rights will trade with RiboGene's Common Stock, unless and until they are
separated upon the occurrence of certain future events. The rights distribution
is not taxable to the stockholders. RiboGene's Board of Directors may terminate
the Rights Plan at any time or redeem the rights prior to the time a person
acquires more than 20 percent of the RiboGene Common Stock. Additional details
regarding the Rights Plan will be outlined in a summary to be mailed to all
stockholders following the Record Date.



<PAGE>   2


RiboGene is a drug discovery company focused on the identification of novel lead
compounds and the development of potential drug candidates for the treatment of
infectious diseases. The Company's drug discovery efforts target infectious
diseases for which the efficacy of existing therapies is being threatened by the
emergence of drug resistance or for which existing therapies have had limited
effectiveness. The Company also has a late stage product, Emitasol(R), under
development for diabetic gastroparesis and chemotherapy-induced delayed onset
nausea and vomiting. RiboGene has alliances with Dainippon Pharmaceutical Co.,
Ltd., Roberts Pharmaceutical Co., ArQule, Inc., and EnzyMed.

Except for the historical information contained herein this press release
contains forward-looking statements that involve risks and uncertainties, which
are discussed in Registration Statement No. 333-38781, as filed by the Company
with the Securities and Exchange Commission. The risk factors and other
information contained in such Registration Statement should be considered in
evaluating the Company's prospects and future financial performance.

          For more information on RiboGene, please contact our website
                              at www.ribogene.com.

                                       ###



<PAGE>   1

                                                                   EXHIBIT 99.2

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


                                 RIBOGENE, INC.

                                       AND

                     AMERICAN STOCK TRANSFER & TRUST COMPANY
                                 AS RIGHTS AGENT


                                RIGHTS AGREEMENT



                            DATED AS OF JULY 1, 1999
- -------------------------------------------------------------------------------




<PAGE>   2

                                RIGHTS AGREEMENT


         THIS RIGHTS AGREEMENT ("Agreement"), dated as of July 1, 1999, between
RIBOGENE, INC., a Delaware corporation (the "Company"), and AMERICAN STOCK
TRANSFER & TRUST COMPANY ("Rights Agent").

         The Board of Directors of the Company has authorized and declared a
dividend of one preferred share purchase right (a "Right") for each Common Share
(as such term is hereinafter defined) outstanding at the close of business on
June 7, 1999 (the "Record Date"), each Right representing the right to purchase
one one-hundredth of a Preferred Share (as such term is hereinafter defined),
upon the terms and subject to the conditions herein set forth, and has further
authorized and directed the issuance of one Right with respect to each Common
Share that shall become outstanding between the Record Date and the earliest to
occur of the Distribution Date, the Redemption Date and the Final Expiration
Date (as such terms are hereinafter defined); provided, however, that Rights may
be issued with respect to Common Shares that shall become outstanding after the
Distribution Date and prior to the earlier of the Redemption Date and the Final
Expiration Date in accordance with the provisions of Section 22 hereof.

         Accordingly, in consideration of the premises and the mutual agreements
herein set forth, the parties hereby agree as follows:

SECTION 1. CERTAIN DEFINITIONS. For purposes of this Agreement, the following
terms have the meanings indicated:

         (a) "ACQUIRING PERSON" shall mean any Person (as such term is
hereinafter defined) who or which, together with all Affiliates and Associates
(as such terms are hereinafter defined) of such Person, shall be the Beneficial
Owner (as such term is hereinafter defined) of 20% or more of the Common Shares
then outstanding. Notwithstanding the foregoing, (A) the term Acquiring Person
shall not include (i) the Company, (ii) any Subsidiary (as such term is
hereinafter defined) of the Company, (iii) any employee benefit or compensation
plan of the Company or any Subsidiary of the Company, (iv) any entity holding
Common Shares for or pursuant to the terms of any such employee benefit or
compensation plan, or (v) an Excluded Stockholder (as such term is hereinafter
defined) and (B) no Person shall become an "Acquiring Person" either (x) as the
result of an acquisition of Common Shares by the Company which, by reducing the
number of shares outstanding, increases the proportionate number of shares
beneficially owned by such Person to 20% or more of the Common Shares then
outstanding; provided, however, that if a Person shall become the Beneficial
Owner of 20% or more of the Common Shares then outstanding by reason of share
purchases by the Company and shall, following written notice from, or public
disclosure by the Company of such share purchases by the Company, become the
Beneficial Owner of any additional Common Shares without the prior consent of
the Company and shall then Beneficially Own more than 20% of the Common Shares
then outstanding, then such Person shall be deemed to be an "Acquiring Person,"
or (y) if the Board of Directors determines in good faith that a Person who
would otherwise be an "Acquiring Person," as defined pursuant to the foregoing
provisions of this paragraph (a), has become such inadvertently, and such Person
divests, as promptly as practicable (as determined in good faith by the Board of
Directors), but in any event within five Business Days, following receipt of



                                       1.
<PAGE>   3

written notice from the Company of such event, of Beneficial Ownership of a
sufficient number of Common Shares so that such Person would no longer be an
Acquiring Person, as defined pursuant to the foregoing provisions of this
paragraph (a), then such Person shall not be deemed to be an "Acquiring Person"
for any purposes of this Agreement; provided, however, that if such Person shall
again become the Beneficial Owner of 20% or more of the Common Shares then
outstanding, such Person shall be deemed an "Acquiring Person," subject to the
exceptions set forth in this Section 1(a).

         (b) "AFFILIATE" and "ASSOCIATE" shall have the respective meanings
ascribed to such terms in Rule 12b-2 of the General Rules and Regulations under
the Securities Exchange Act of 1934, as amended (the "Exchange Act"), as in
effect on the date of this Agreement.

         (c) A Person shall be deemed the "BENEFICIAL OWNER" of and shall be
deemed to "beneficially own" any securities:

              (i) which such Person or any of such Person's Affiliates or
Associates is deemed to beneficially own, within the meaning of Rule 13d-3 of
the General Rules and Regulations under the Exchange Act as in effect on the
date of this Rights Agreement;

              (ii) which such Person or any of such Person's Affiliates or
Associates has (A) the right to acquire (whether such right is exercisable
immediately or only after the passage of time) pursuant to any agreement,
arrangement or understanding (other than customary agreements with and between
underwriters and selling group members with respect to a bona fide public
offering of securities), or upon the exercise of conversion rights, exchange
rights, rights (other than these Rights), warrants or options, or otherwise;
provided, however, that a Person shall not be deemed the Beneficial Owner of, or
to beneficially own, securities tendered pursuant to a tender or exchange offer
made by or on behalf of such Person or any of such Person's Affiliates or
Associates until such tendered securities are accepted for purchase or exchange;
or (B) the right to vote pursuant to any agreement, arrangement or
understanding; provided, however, that a Person shall not be deemed the
Beneficial Owner of, or to beneficially own, any security if the agreement,
arrangement or understanding to vote such security (1) arises solely from a
revocable proxy or consent given to such Person in response to a public proxy or
consent solicitation made pursuant to, and in accordance with, the applicable
rules and regulations promulgated under the Exchange Act and (2) is not also
then reportable on Schedule 13D under the Exchange Act (or any comparable or
successor report); or

              (iii) which are beneficially owned, directly or indirectly, by any
other Person with which such Person or any of such Person's Affiliates or
Associates has any agreement, arrangement or understanding (other than customary
agreements with and between underwriters and selling group members with respect
to a bona fide public offering of securities) for the purpose of acquiring,
holding, voting (except to the extent contemplated by the proviso to Section
1(c)(ii)(B) hereof) or disposing of any securities of the Company.

         Notwithstanding anything in this definition of Beneficial Ownership to
the contrary, the phrase, "then outstanding," when used with reference to a
Person's Beneficial Ownership of securities of the Company, shall mean the
number of such securities then issued and outstanding



                                       2.
<PAGE>   4

together with the number of such securities not then actually issued and
outstanding which such Person would be deemed to own beneficially hereunder.

         (d) "BUSINESS DAY" shall mean any day other than a Saturday, a Sunday,
or a day on which banking institutions in the State of New York are authorized
or obligated by law or executive order to close.

         (e) "CLOSE OF BUSINESS" on any given date shall mean 5:00 p.m., Eastern
Standard Time, on such date; provided, however, that if such date is not a
Business Day it shall mean 5:00 p.m., Eastern Standard Time, on the next
succeeding Business Day.

         (f) "COMMON SHARES" shall mean the shares of common stock, par value
$.001 per share, of the Company; provided, however, that, "Common Shares," when
used in this Agreement in connection with a specific reference to any Person
other than the Company, shall mean the capital stock (or equity interest) with
the greatest voting power of such other Person or, if such other Person is a
Subsidiary of another Person, the Person or Persons which ultimately control
such first-mentioned Person.

         (g) "DISTRIBUTION DATE" shall have the meaning set forth in Section 3
hereof.

         (h) "EXCLUDED STOCKHOLDERS" shall mean (i) Dr. Lindsay Rosenwald,
Paramount Capital Asset Management, Inc., the Aries Domestic Fund, L.P. and The
Aries Trust (including their Affiliates and Associates), provided, that Dr.
Lindsay Rosenwald, Paramount Capital Asset Management, Inc., the Aries Domestic
Fund, L.P. and The Aries Trust (including their Affiliates and Associates) shall
not be an Excluded Stockholder if Dr. Lindsay Rosenwald, Paramount Capital Asset
Management, Inc., the Aries Domestic Fund, L.P. and The Aries Trust (including
their Affiliates and Associates) become the Beneficial Owner of an aggregate of
more than 22% of the outstanding Common Shares without the prior approval of the
Board of Directors of the Company; and (ii) Roberts Pharmaceutical Corporation;
provided, that Roberts Pharmaceutical Corporation shall not be an Excluded
Stockholder if Roberts Pharmaceutical Corporation becomes the Beneficial Owner
of more than 22% of the outstanding Common Shares without the prior approval of
the Board of Directors of the Company.

         (i) "FINAL EXPIRATION DATE" shall have the meaning set forth in
Section 7 hereof.

         (j) "INTERESTED STOCKHOLDER" shall mean any Acquiring Person or any
Affiliate or Associate of an Acquiring Person or any other Person in which any
such Acquiring Person, Affiliate or Associate has an interest, or any other
Person acting directly or indirectly on behalf of or in concert with any such
Acquiring Person, Affiliate or Associate.

         (k) "PERSON" shall mean any individual, firm, corporation or other
entity, and shall include any successor (by merger or otherwise) of such entity.

         (l) "PREFERRED SHARES" shall mean shares of Series B Junior
Participating Preferred Stock, par value $.001 per share, of the Company having
the designations and the powers, preferences and rights, and the qualifications,
limitations and restrictions set forth in the Form of Certificate of Designation
attached to this Agreement as Exhibit A.



                                       3.
<PAGE>   5

         (m) "PURCHASE PRICE" shall have the meaning set forth in Section 7(b)
hereof.

         (n) "REDEMPTION DATE" shall have the meaning set forth in Section 7
hereof.

         (o) "SHARES ACQUISITION DATE" shall mean the first date of public
announcement by the Company or an Acquiring Person that an Acquiring Person has
become such provided, however that, if such Person is determined not to have
become an Acquiring Person pursuant to clause (y) of Subsection 1(a)(B) hereof,
then no Shares Acquisition Date shall be deemed to have occurred.

         (p) "SUBSIDIARY" of any Person shall mean any corporation or other
entity of which a majority of the voting power of the voting equity securities
or equity interest is owned, directly or indirectly, by such Person.

         (q) "TRANSACTION" shall mean any merger, consolidation or sale of
assets described in Section 13(a) hereof or any acquisition of Common Shares
which would result in a Person becoming an Acquiring Person or a Principal Party
(as such term is hereinafter defined).

         (r) "TRANSACTION PERSON" with respect to a Transaction shall mean (i)
any Person who (x) is or will become an Acquiring Person or a Principal Party
(as such term is hereinafter defined) if the Transaction were to be consummated
and (y) directly or indirectly proposed or nominated a director of the Company
which director is in office at the time of consideration of the Transaction, or
(ii) an Affiliate or Associate of such a Person.

SECTION 2. APPOINTMENT OF RIGHTS AGENT. The Company hereby appoints the Rights
Agent to act as agent for the Company in accordance with the terms and
conditions hereof, and the Rights Agent hereby accepts such appointment. The
Company may from time to time appoint such co-Rights Agents as it may deem
necessary or desirable.

SECTION 3. ISSUE OF RIGHT CERTIFICATES.

         (a) Until the earlier of (i) the Shares Acquisition Date or (ii) the
tenth Business Day (or such later date as may be determined by action of the
Board of Directors prior to such time as any Person becomes an Acquiring Person)
after the date of the commencement (determined in accordance with Rule 14d-2
under the Exchange Act) by any Person (other than the Company, any Subsidiary of
the Company, any employee benefit plan of the Company or of any Subsidiary of
the Company or any entity holding Common Shares for or pursuant to the terms of
any such plan) of, or of the first public announcement of the intention of any
Person (other than the Company, any Subsidiary of the Company, any employee
benefit plan of the Company or of any Subsidiary of the Company or any entity
holding Common Shares for or pursuant to the terms of any such plan) to
commence, a tender or exchange offer (which intention to commence remains in
effect for five Business Days after such announcement), the consummation of
which would result in any Person becoming an Acquiring Person (including any
such date which is after the date of this Agreement and prior to the issuance of
the Rights, the earlier of such dates being herein referred to as the
"Distribution Date"), (x) the Rights will be evidenced by the certificates for
Common Shares registered in the names of the holders thereof (which certificates
shall also be deemed to be Right Certificates) and not by separate Right
Certificates, and (y) the Rights (and the right to receive Right Certificates
therefor) will be transferable only in connection with



                                       4.
<PAGE>   6

the transfer of Common Shares. As soon as practicable after the Distribution
Date, the Company will prepare and execute, the Rights Agent will countersign,
and the Company will send or cause to be sent (and the Rights Agent will, if
requested, send) by first-class, insured, postage-prepaid mail, to each record
holder of Common Shares as of the Close of Business on the Distribution Date, at
the address of such holder shown on the records of the Company, a Right
Certificate, in substantially the form of Exhibit B hereto (a "Right
Certificate"), evidencing one Right for each Common Share so held, subject to
the adjustment provisions of Section 11 of this Rights Agreement. As of the
Distribution Date, the Rights will be evidenced solely by such Right
Certificates.

         (b) On the Record Date, or as soon as practicable thereafter, the
Company will send (directly or through the Rights Agent or its transfer agent) a
copy of a Summary of Rights to Purchase Preferred Shares, in substantially the
form of Exhibit C hereto (the "Summary of Rights"), by first-class,
postage-prepaid mail, to each record holder of Common Shares as of the Close of
Business on the Record Date, at the address of such holder shown on the records
of the Company. With respect to certificates for Common Shares outstanding as of
the Record Date, until the Distribution Date, the Rights will be evidenced by
such certificates registered in the names of the holders thereof. Until the
Distribution Date (or the earlier of the Redemption Date and the Final
Expiration Date), the surrender for transfer of any certificate for Common
Shares outstanding on the Record Date shall also constitute the transfer of the
Rights associated with the Common Shares represented thereby.

         (c) Certificates for Common Shares which become outstanding (including,
without limitation, reacquired Common Shares referred to in the last sentence of
this paragraph (c)) after the Record Date but prior to the earliest of the
Distribution Date, the Redemption Date or the Final Expiration Date shall have
impressed on, printed on, written on or otherwise affixed to them the following
legend:

                  This certificate also evidences and entitles the holder hereof
         to certain rights as set forth in a Rights Agreement between RiboGene,
         Inc. (the "Company") and American Stock Transfer as Rights Agent (the
         "Rights Agent"), dated as of July 1, 1999, as amended from time to time
         (the "Rights Agreement"), the terms of which are hereby incorporated
         herein by reference and a copy of which is on file at the principal
         executive offices of the Company. Under certain circumstances, as set
         forth in the Rights Agreement, such Rights will be evidenced by
         separate certificates and will no longer be evidenced by this
         certificate. The Company will mail to the holder of this certificate a
         copy of the Rights Agreement without charge after receipt of a written
         request therefor. As described in the Rights Agreement, Rights issued
         to any Person who becomes an Acquiring Person or an Affiliate or
         Associate thereof (as defined in the Rights Agreement) and certain
         related persons, whether currently held by or on behalf of such Person
         or by any subsequent holder, shall become null and void.

         With respect to such certificates containing the foregoing legend,
until the Distribution Date, the Rights associated with the Common Shares
represented by such certificates shall be evidenced by such certificates alone,
and the surrender for transfer of any such certificate shall also constitute the
transfer of the Rights associated with the Common Shares represented



                                       5.
<PAGE>   7

thereby. In the event that the Company purchases or acquires any Common Shares
after the Record Date but prior to the Distribution Date, any Rights associated
with such Common Shares shall be deemed canceled and retired so that the Company
shall not be entitled to exercise any Rights associated with the Common Shares
which are no longer outstanding. Notwithstanding this Section 3(c), the omission
of a legend shall not affect the enforceability of any part of this Rights
Agreement or the rights of any holder of the Rights.

SECTION 4. FORM OF RIGHT CERTIFICATES.

         (a) The Right Certificates (and the form of election to purchase
Preferred Shares, the form of assignment and the form of certification to be
printed on the reverse thereof) shall be substantially the same as Exhibit B
hereto and may have such marks of identification or designation and such
legends, summaries or endorsements printed thereon as the Company may deem
appropriate and as are not inconsistent with the provisions of this Agreement,
or as may be required to comply with any applicable law or with any rule or
regulation made pursuant thereto or with any rule or regulation of any stock
exchange or quotation system on which the Rights may from time to time be
listed, or to conform to usage. Subject to the provisions of Sections 7, 11 and
22 hereof, the Right Certificates shall entitle the holders thereof to purchase
such number of one one-hundredths of a Preferred Share as shall be set forth
therein at the price per one one-hundredth of a Preferred Share set forth
therein (the "Purchase Price"), but the number of such one one-hundredths of a
Preferred Share and the Purchase Price shall be subject to adjustment as
provided herein.

         (b) Any Right Certificate issued pursuant to Section 3(a) or Section 22
hereof that represents Rights which are null and void pursuant to Section
11(a)(ii) hereof and any Right Certificate issued pursuant to Section 6 or
Section 11 hereof upon transfer, exchange, replacement or adjustment of any
other Right Certificate referred to in this sentence, shall contain (to the
extent feasible) the following legend:

         The Rights represented by this Right Certificate are or were
beneficially owned by a Person who was or became an Acquiring Person or an
Affiliate or Associate of an Acquiring Person (as such terms are defined in the
Rights Agreement). Accordingly, this Right Certificate and the Rights
represented hereby are null and void.

         The provisions of Section 11(a)(ii) hereof shall be operative whether
or not the foregoing legend is contained on any such Right Certificate.

SECTION 5. COUNTERSIGNATURE AND REGISTRATION. The Right Certificates shall be
executed on behalf of the Company by its Chairman of the Board, its Chief
Executive Officer, its President, its Vice Chairman of the Board, its Chief
Financial Officer, or any of its Vice Presidents, either manually or by
facsimile signature, shall have affixed thereto the Company's seal or a
facsimile thereof, and shall be attested by the Secretary or an Assistant
Secretary of the Company, either manually or by facsimile signature. The Right
Certificates shall be manually countersigned by the Rights Agent and shall not
be valid for any purpose unless countersigned. In case any officer of the
Company who shall have signed any of the Right Certificates shall cease to be
such officer of the Company before countersignature by the Rights Agent and
issuance and delivery by the Company, such Right Certificates, nevertheless, may
be



                                       6.
<PAGE>   8

countersigned by the Rights Agent and issued and delivered by the Company
with the same force and effect as though the person who signed such Right
Certificates had not ceased to be such officer of the Company; and any Right
Certificate may be signed on behalf of the Company by any person who, at the
actual date of the execution of such Right Certificate, shall be a proper
officer of the Company to sign such Right Certificate, although at the date of
the execution of this Agreement any such person was not such an officer.

         Following the Distribution Date, the Rights Agent will keep or cause to
be kept, at its office designated for such purpose, books for registration and
transfer of the Right Certificates issued hereunder. Such books shall show the
names and addresses of the respective holders of the Right Certificates, the
number of Rights evidenced on its face by each of the Right Certificates and the
date of each of the Right Certificates.

SECTION 6. TRANSFER, SPLIT UP, COMBINATION AND EXCHANGE OF RIGHT CERTIFICATES;
MUTILATED, DESTROYED, LOST OR STOLEN RIGHT CERTIFICATES. Subject to the
provisions of Section 11(a)(ii), Section 14 and Section 24 hereof, at any time
after the Close of Business on the Distribution Date, and at or prior to the
Close of Business on the earlier of the Redemption Date or the Final Expiration
Date, any Right Certificate or Right Certificates may be transferred, split up,
combined or exchanged for another Right Certificate or Right Certificates,
entitling the registered holder to purchase a like number of one one-hundredths
of a Preferred Share as the Right Certificate or Right Certificates surrendered
then entitled such holder to purchase. Any registered holder desiring to
transfer, split up, combine or exchange any Right Certificate or Right
Certificates shall make such request in writing delivered to the Rights Agent,
and shall surrender the Right Certificate or Right Certificates to be
transferred, split up, combined or exchanged at the office of the Rights Agent
designated for such purpose. Neither the Rights Agent nor the Company shall be
obligated to take any action whatsoever with respect to the transfer of any such
surrendered Right Certificate until the registered holder shall have completed
and signed the certificate contained in the form of assignment on the reverse
side of such Right Certificate and shall have provided such additional evidence
of the identity of the Beneficial Owner (or former Beneficial Owner) or
Affiliates or Associates thereof as the Company shall reasonably request.
Thereupon the Rights Agent shall, subject to Section 11(a)(ii), Section 14 and
Section 24 hereof, countersign and deliver to the person entitled thereto a
Right Certificate or Right Certificates, as the case may be, as so requested.
The Company may require payment of a sum sufficient to cover any tax or
governmental charge that may be imposed in connection with any transfer, split
up, combination or exchange of Right Certificates.

         Upon receipt by the Company and the Rights Agent of evidence reasonably
satisfactory to them of the loss, theft, destruction or mutilation of a Right
Certificate, and, in case of loss, theft or destruction, of indemnity or
security reasonably satisfactory to them, and, at the Company's request,
reimbursement to the Company and the Rights Agent of all reasonable expenses
incidental thereto, and upon surrender to the Rights Agent and cancellation of
the Right Certificate if mutilated, the Company will issue, execute and deliver
a new Right Certificate of like tenor to the Rights Agent for countersignature
and delivery to the registered holder in lieu of the Right Certificate so lost,
stolen, destroyed or mutilated.



                                       7.
<PAGE>   9

         Notwithstanding any other provisions hereof, the Company and the Rights
Agent may amend this Rights Agreement to provide for uncertificated Rights in
addition to or in place of Rights evidenced by Rights Certificates.

SECTION 7. EXERCISE OF RIGHTS; PURCHASE PRICE; EXPIRATION DATE OF RIGHTS.

         (a) The registered holder of any Right Certificate may exercise the
Rights evidenced thereby (except as otherwise provided herein) in whole or in
part at any time after the Distribution Date upon surrender of the Right
Certificate, with the form of election to purchase on the reverse side thereof
duly executed, to the Rights Agent at the office of the Rights Agent designated
for such purpose, together with payment of the Purchase Price for each one
one-hundredth of a Preferred Share (or such other number of shares or other
securities) as to which the Rights are exercised, at or prior to the earliest of
(i) the Close of Business on June 30, 2009 (the "Final Expiration Date"), (ii)
the time at which the Rights are redeemed as provided in Section 23 hereof (the
"Redemption Date"), or (iii) the time at which such Rights are exchanged as
provided in Section 24 hereof.

         (b) The purchase price (the "Purchase Price") for each one
one-hundredth of a Preferred Share pursuant to the exercise of a Right shall
initially be $25.00 and shall be subject to adjustment from time to time as
provided in Sections 11 and 13 hereof and shall be payable in lawful money of
the United States of America in accordance with paragraph (c) below.

         (c) Upon receipt of a Right Certificate representing exercisable
Rights, with the form of election to purchase duly executed, accompanied by
payment of the Purchase Price for the shares to be purchased and an amount equal
to any applicable transfer tax required to be paid by the holder of such Right
Certificate in accordance with Section 9 hereof by certified check, cashier's
check, bank draft or money order payable to the order of the Company, the Rights
Agent shall thereupon promptly (i) (A) requisition from any transfer agent for
the Preferred Shares certificates for the number of Preferred Shares to be
purchased and the Company hereby irrevocably authorizes its transfer agent to
comply with all such requests, or (B) if the Company, in its sole discretion,
shall have elected to deposit the Preferred Shares issuable upon exercise of the
Rights hereunder into a depository, requisition from the depositary agent
depositary receipts representing such number of one one-hundredths of a
Preferred Share as are to be purchased (in which case certificates for the
Preferred Shares represented by such receipts shall be deposited by the transfer
agent with the depositary agent) and the Company hereby directs the depositary
agent to comply with such request, (ii) when appropriate, requisition from the
Company the amount of cash to be paid in lieu of issuance of fractional shares
in accordance with Section 14 hereof, (iii) after receipt of such certificates
or depositary receipts, cause the same to be delivered to or upon the order of
the registered holder of such Right Certificate, registered in such name or
names as may be designated by such holder and (iv) when appropriate, after
receipt, deliver such cash to or upon the order of the registered holder of such
Right Certificate. In the event that the Company is obligated to issue
securities of the Company other than Preferred Shares (including Common Shares)
of the Company pursuant to Section 11(a) hereof, the Company will make all
arrangements necessary so that such other securities are available for
distribution by the Rights Agent, if and when appropriate.



                                       8.
<PAGE>   10

         In addition, in the case of an exercise of the Rights by a holder
pursuant to Section 11(a)(ii) hereof, the Rights Agent shall return such Right
Certificate to the registered holder thereof after imprinting, stamping or
otherwise indicating thereon that the rights represented by such Right
Certificate no longer include the rights provided by Section 11(a)(ii) hereof,
and, if fewer than all the Rights represented by such Right Certificate were so
exercised, the Rights Agent shall indicate on the Right Certificate the number
of Rights represented thereby which continue to include the rights provided by
Section 11(a)(ii) hereof.

         (d) In case the registered holder of any Right Certificate shall
exercise fewer than all the Rights evidenced thereby, a new Right Certificate
evidencing Rights equivalent to the Rights remaining unexercised shall be issued
by the Rights Agent to the registered holder of such Right Certificate or to his
duly authorized assigns, subject to the provisions of Section 14 hereof.

         (e) The Company covenants and agrees that it will cause to be reserved
and kept available out of its authorized and unissued Preferred Shares or any
Preferred Shares held in its treasury, the number of Preferred Shares that will
be sufficient to permit the exercise in full of all outstanding Rights in
accordance with this Section 7.

         (f) Notwithstanding anything in this Agreement to the contrary, neither
the Rights Agent nor the Company shall be obligated to undertake any action with
respect to a registered holder upon the occurrence of any purported exercise as
set forth in this Section 7 unless such registered holder shall have (i)
completed and signed the certification following the form of election to
purchase set forth on the reverse side of the Rights Certificate surrendered for
such exercise and (ii) provided such additional evidence of the identity of the
Beneficial Owner (or former Beneficial Owner) or Affiliates or Associates
thereof as the Company shall reasonably request.

SECTION 8. CANCELLATION AND DESTRUCTION OF RIGHT CERTIFICATES. All Right
Certificates surrendered for the purpose of exercise, transfer, split up,
combination or exchange shall, if surrendered to the Company or to any of its
agents, be delivered to the Rights Agent for cancellation or in canceled form,
or, if delivered or surrendered to the Rights Agent, shall be canceled by it,
and no Right Certificates shall be issued in lieu thereof except as expressly
permitted by any of the provisions of this Agreement. The Company shall deliver
to the Rights Agent for cancellation and retirement, and the Rights Agent shall
so cancel and retire, any other Right Certificate purchased or acquired by the
Company otherwise than upon the exercise thereof. The Rights Agent shall deliver
all canceled Right Certificates to the Company approximately one and one-half
years after the cancellation date, or shall, at the written request of the
Company, destroy such canceled Right Certificates, and in such case shall
deliver a certificate of destruction thereof to the Company.

SECTION 9. AVAILABILITY OF PREFERRED SHARES. The Company covenants and agrees
that so long as the Preferred Shares (and, after the time a person becomes an
Acquiring Person, Common Shares or any other securities) issuable upon the
exercise of the Rights may be listed on any national securities exchange or
quotation system, the Company shall use its best efforts to cause, from and
after such time as the Rights become exercisable, all shares reserved for such
issuance to be listed on such exchange or quotation system upon official notice
of issuance upon such exercise.



                                       9.
<PAGE>   11

         The Company covenants and agrees that it will take all such action as
may be necessary to ensure that all Preferred Shares (or Common Shares and other
securities, as the case may be) delivered upon exercise of Rights shall, at the
time of delivery of the certificates for such Preferred Shares (subject to
payment of the Purchase Price), be duly and validly authorized and issued and
fully paid and nonassessable shares or other securities.

         The Company further covenants and agrees that it will pay when due and
payable any and all federal and state transfer taxes and charges which may be
payable in respect of the issuance or delivery of the Right Certificates or of
any Preferred Shares upon the exercise of Rights. The Company shall not,
however, be required to pay any transfer tax which may be payable in respect of
any transfer or delivery of Right Certificates to a person other than, or the
issuance or delivery of certificates or depositary receipts for the Preferred
Shares in a name other than that of, the registered holder of the Right
Certificate evidencing Rights surrendered for exercise or to issue or to deliver
any certificates or depositary receipts for Preferred Shares upon the exercise
of any Rights until any such tax shall have been paid (any such tax being
payable by the holder of such Right Certificate at the time of surrender) or
until it has been established to the Company's reasonable satisfaction that no
such tax is due.

         As soon as practicable after the Distribution Date, the Company shall
use its best efforts to:

               (i) prepare and file a registration statement under the
Securities Act of 1933, as amended (the "Act"), with respect to the Rights and
the securities purchasable upon exercise of the Rights on an appropriate form,
will use its best efforts to cause such registration statement to become
effective as soon as practicable after such filing and will use its best efforts
to cause such registration statement to remain effective (with a prospectus at
all times meeting the requirements of the Act) until the Final Expiration Date;
and

               (ii) use its best efforts to qualify or register the Rights and
the securities purchasable upon exercise of the Rights under the blue sky laws
of such jurisdictions as may be necessary or appropriate.

SECTION 10. PREFERRED SHARES RECORD DATE. Each person in whose name any
certificate for Preferred Shares or other securities is issued upon the exercise
of Rights shall for all purposes be deemed to have become the holder of record
of the Preferred Shares or other securities represented thereby on, and such
certificate shall be dated, the date upon which the Right Certificate evidencing
such Rights was duly surrendered with the forms of election and certification
duly executed and payment of the Purchase Price (and any applicable transfer
taxes) was made; provided, however, that if the date of such surrender and
payment is a date upon which the Preferred Shares or other securities transfer
books of the Company are closed, such person shall be deemed to have become the
record holder of such shares on, and such certificate shall be dated, the next
succeeding Business Day on which the Preferred Shares or other securities
transfer books of the Company are open. Prior to the exercise of the Rights
evidenced thereby, the holder of a Right Certificate, as such, shall not be
entitled to any rights of a holder of Preferred Shares for which the Rights
shall be exercisable, including, without limitation, the right to vote, to
receive dividends or other distributions or to exercise any preemptive rights,
and shall



                                      10.
<PAGE>   12

not be entitled to receive any notice of any proceedings of the Company, except
as provided herein.

SECTION 11. ADJUSTMENT OF PURCHASE PRICE, NUMBER OF SHARES OR NUMBER OF RIGHTS.
The Purchase Price, the number of Preferred Shares covered by each Right and the
number of Rights outstanding are subject to adjustment from time to time as
provided in this Section 11.

     (a)

               (i) In the event the Company shall at any time after the date of
this Agreement (A) declare a dividend on the Preferred Shares payable in
Preferred Shares, (B) subdivide the outstanding Preferred Shares, (C) combine
the outstanding Preferred Shares into a smaller number of Preferred Shares or
(D) issue any shares of its capital stock in a reclassification of the Preferred
Shares (including any such reclassification in connection with a consolidation
or merger in which the Company is the continuing or surviving corporation),
except as otherwise provided in this Section 11(a), the Purchase Price in effect
at the time of the record date for such dividend or of the effective date of
such subdivision, combination or reclassification, and the number and kind of
shares of capital stock issuable on such date, shall be proportionately adjusted
so that the holder of any Right exercised after such time shall be entitled to
receive the aggregate number and kind of shares of capital stock which, if such
Right had been exercised immediately prior to such date and at a time when the
Preferred Shares transfer books of the Company were open, such holder would have
owned upon such exercise and been entitled to receive by virtue of such
dividend, subdivision, combination or reclassification; provided, however, that
in no event shall the consideration to be paid upon the exercise of one Right be
less than the aggregate par value of the shares of capital stock of the Company
issuable upon exercise of one Right. If an event occurs which would require an
adjustment under both Section 11(a)(i) and Section 11(a)(ii) hereof, the
adjustment provided for in this Section 11(a)(i) shall be in addition to, and
shall be made prior to any adjustment required pursuant to Section 11(a)(ii)
hereof.

               (ii) Subject to Section 24 hereof and the provisions of the next
paragraph of this Section 11(a)(ii), in the event any Person shall become an
Acquiring Person, each holder of a Right shall, for a period of 60 days after
the later of such time any Person becomes an Acquiring Person or the effective
date of an appropriate registration statement under the Act pursuant to Section
9 hereof (provided, however that, if at any time prior to the expiration or
termination of the Rights there shall be a temporary restraining order, a
preliminary injunction, an injunction, or temporary suspension by the Board of
Directors, or similar obstacle to exercise of the Rights (the "Injunction")
which prevents exercise of the Rights, a new 60-day period shall commence on the
date the Injunction is removed), have a right to receive, upon exercise thereof
at a price equal to the then current Purchase Price multiplied by the number of
one one-hundredths of a Preferred Share for which a Right is then exercisable,
in accordance with the terms of this Agreement and in lieu of Preferred Shares,
such number of Common Shares as shall equal the result obtained by (A)
multiplying the then current Purchase Price by the number of one one-hundredths
of a Preferred Share for which a Right is then exercisable and dividing that
product by (B) 50% of the then current per share market price of the Common
Shares (determined pursuant to Section 11(d) hereof) on the date such Person
became an Acquiring Person; provided, however, that if the



                                      11.
<PAGE>   13

transaction that would otherwise give rise to the foregoing adjustment is also
subject to the provisions of Section 13 hereof, then only the provisions of
Section 13 hereof shall apply and no adjustment shall be made pursuant to this
Section 11(a)(ii). In the event that any Person shall become an Acquiring Person
and the Rights shall then be outstanding, the Company shall not take any action
which would eliminate or diminish the benefits intended to be afforded by the
Rights.

         Notwithstanding anything in this Agreement to the contrary, from and
after the time any Person becomes an Acquiring Person, any Rights beneficially
owned by (i) such Acquiring Person or an Associate or Affiliate of such
Acquiring Person, (ii) a transferee of such Acquiring Person (or of any such
Associate or Affiliate) who becomes a transferee after the Acquiring Person
became such, or (iii) a transferee of such Acquiring Person (or of any such
Associate or Affiliate) who becomes a transferee prior to or concurrently with
the Acquiring Person's becoming such and receives such Rights pursuant to either
(A) a transfer (whether or not for consideration) from the Acquiring Person to
holders of equity interests in such Acquiring Person or to any Person with whom
the Acquiring Person has any continuing agreement, arrangement or understanding
regarding the transferred Rights or (B) a transfer which the Board of Directors
of the Company has determined is part of a plan, arrangement or understanding
which has as a primary purpose or effect the avoidance of this Section
11(a)(ii), shall become null and void without any further action and no holder
of such Rights shall have any rights whatsoever with respect to such Rights,
whether under any provision of this Agreement or otherwise. The Company shall
use all reasonable efforts to insure that the provisions of this Section
11(a)(ii) and Section 4(b) hereof are complied with, but shall have no liability
to any holder of Right Certificates or other Person as a result of its failure
to make any determinations with respect to an Acquiring Person or its
Affiliates, Associates or transferees hereunder. No Right Certificate shall be
issued at any time upon the transfer of any Rights to an Acquiring Person whose
Rights would be void pursuant to the preceding sentence or any Associate or
Affiliate thereof or to any nominee of such Acquiring Person, Associate or
Affiliate; and any Right Certificate delivered to the Rights Agent for transfer
to an Acquiring Person whose Rights would be void pursuant to the preceding
sentence shall be canceled.

               (iii) In lieu of issuing Common Shares in accordance with Section
11(a)(ii) hereof, the Company may, if a majority of the Board of Directors then
in office determines that such action is necessary or appropriate and not
contrary to the interests of holders of Rights, elect to (and, in the event that
the Board of Directors has not exercised the exchange right contained in Section
24(c) hereof and there are not sufficient treasury shares and authorized but
unissued Common Shares to permit the exercise in full of the Rights in
accordance with the foregoing subparagraph (ii), the Company shall) take all
such action as may be necessary to authorize, issue or pay, upon the exercise of
the Rights, cash (including by way of a reduction of the Purchase Price),
property, Common Shares, other securities or any combination thereof having an
aggregate value equal to the value of the Common Shares which otherwise would
have been issuable pursuant to Section 11(a)(ii) hereof, which aggregate value
shall be determined by a nationally recognized investment banking firm selected
by a majority of the Board of Directors then in office. For purposes of the
preceding sentence, the value of the Common Shares shall be determined pursuant
to Section 11(d) hereof. Any such election by the Board of Directors must be
made within 60 days following the date on which the event described in Section
11(a)(ii) hereof shall have occurred. Following the occurrence of the event
described in Section 11(a)(ii)



                                      12.
<PAGE>   14

hereof, a majority of the Board of Directors then in office may suspend the
exercisability of the Rights for a period of up to 60 days following the date on
which the event described in Section 11(a)(ii) hereof shall have occurred to the
extent that such directors have not determined whether to exercise their rights
of election under this Section 11(a)(iii). In the event of any such suspension,
the Company shall issue a public announcement stating that the exercisability of
the Rights has been temporarily suspended.

         (b) In case the Company shall fix a record date for the issuance of
rights, options or warrants to all holders of Preferred Shares entitling them to
subscribe for or purchase Preferred Shares (or shares having the same
designations and the powers, preferences and rights, and the qualifications,
limitations and restrictions as the Preferred Shares ("equivalent preferred
shares")) or securities convertible into Preferred Shares or equivalent
preferred shares at a price per Preferred Share or equivalent preferred share
(or having a conversion price per share, if a security convertible into
Preferred Shares or equivalent preferred shares) less than the then current per
share market price of the Preferred Shares (as such term is hereinafter defined)
on such record date, the Purchase Price to be in effect after such record date
shall be determined by multiplying the Purchase Price in effect immediately
prior to such record date by a fraction, the numerator of which shall be the
number of Preferred Shares outstanding on such record date plus the number of
Preferred Shares which the aggregate offering price of the total number of
Preferred Shares and/or equivalent preferred shares so to be offered (and/or the
aggregate initial conversion price of the convertible securities so to be
offered) would purchase at such current market price and the denominator of
which shall be the number of Preferred Shares outstanding on such record date
plus the number of additional Preferred Shares and/or equivalent preferred
shares to be offered for subscription or purchase (or into which the convertible
securities so to be offered are initially convertible); provided, however, that
in no event shall the consideration to be paid upon the exercise of one Right be
less than the aggregate par value of the shares of capital stock of the Company
issuable upon exercise of one Right. In case such subscription price may be paid
in a consideration part or all of which shall be in a form other than cash, the
value of such consideration shall be as determined in good faith by the Board of
Directors of the Company, whose determination shall be described in a statement
filed with the Rights Agent. Preferred Shares owned by or held for the account
of the Company shall not be deemed outstanding for the purpose of any such
computation. Such adjustment shall be made successively whenever such a record
date is fixed; and in the event that such rights, options or warrants are not so
issued, the Purchase Price shall be adjusted to be the Purchase Price which
would then be in effect if such record date had not been fixed.

         (c) In case the Company shall fix a record date for the making of a
distribution to all holders of the Preferred Shares (including any such
distribution made in connection with a consolidation or merger in which the
Company is the continuing or surviving corporation) of evidences of indebtedness
or assets (other than a regular quarterly cash dividend or a dividend payable in
Preferred Shares) or subscription rights or warrants (excluding those referred
to in Section 11(b) hereof), the Purchase Price to be in effect after such
record date shall be determined by multiplying the Purchase Price in effect
immediately prior to such record date by a fraction, the numerator of which
shall be the then current per share market price of the Preferred Shares (as
such term is hereinafter defined) on such record date, less the fair market
value (as determined in good faith by the Board of Directors of the Company,
whose determination shall be described in a statement filed with the Rights
Agent) of the portion of the



                                      13.
<PAGE>   15

assets or evidences of indebtedness so to be distributed or of such subscription
rights or warrants applicable to one Preferred Share and the denominator of
which shall be such current per share market price of the Preferred Shares;
provided, however, that in no event shall the consideration to be paid upon the
exercise of one Right be less than the aggregate par value of the shares of
capital stock of the Company to be issued upon exercise of one Right. Such
adjustments shall be made successively whenever such a record date is fixed; and
in the event that such distribution is not so made, the Purchase Price shall
again be adjusted to be the Purchase Price which would then be in effect if such
record date had not been fixed.

         (d)

               (i) For the purpose of any computation hereunder, the "current
per share market price" of any security (a "Security" for the purpose of this
Section 11(d)(i)) on any date shall be deemed to be the average of the daily
closing prices per share of such Security for the 30 consecutive Trading Days
(as such term is hereinafter defined) immediately prior to such date; provided,
however, that in the event that the current per share market price of the
Security is determined during a period following the announcement by the issuer
of such Security of (A) a dividend or distribution on such Security payable in
shares of such Security or securities convertible into such shares, or (B) any
subdivision, combination or reclassification of such Security or securities
convertible into such shares, or (C) any subdivision, combination or
reclassification of such Security and prior to the expiration of 30 Trading Days
after the ex-dividend date for such dividend or distribution, or the record date
for such subdivision, combination or reclassification, then, and in each such
case, the current per share market price shall be appropriately adjusted to
reflect the current market price per share equivalent of such Security. The
closing price for each day shall be the last sale price, regular way, or, in
case no such sale takes place on such day, the average of the closing bid and
asked prices, regular way, in either case as reported in the principal
consolidated transaction reporting system with respect to securities listed or
admitted to trading on the New York Stock Exchange or, if the Security is not
listed or admitted to trading on the New York Stock Exchange, as reported in the
principal consolidated transaction reporting system with respect to securities
listed on the principal national securities exchange on which the Security is
listed or admitted to trading or as reported on the Nasdaq National Market or,
if the Security is not listed or admitted to trading on any national securities
exchange or reported on the Nasdaq National Market, the last quoted price or, if
not so quoted, the average of the high bid and low asked prices in the
over-the-counter market, as reported by the National Association of Securities
Dealers, Inc. Automated Quotations System ("Nasdaq") or such other system then
in use, or, if on any such date the Security is not quoted by any such
organization, the average of the closing bid and asked prices as furnished by a
professional market maker making a market in the Security selected by the Board
of Directors of the Company or, if on any such date no professional market maker
is making a market in the Security, the price as determined in good faith by the
Board of Directors. The term "Trading Day" shall mean a day on which the
principal national securities exchange on which the Security is listed or
admitted to trading is open for the transaction of business or, if the Security
is not listed or admitted to trading on any national securities exchange, a
Business Day.

               (ii) For the purpose of any computation hereunder, the "current
per share market price" of the Preferred Shares shall be determined in
accordance with the method set forth in Section 11(d)(i) hereof. If the
Preferred Shares are not publicly traded, the "current per



                                      14.
<PAGE>   16

share market price" of the Preferred Shares shall be conclusively deemed to be
the current per share market price of the Common Shares as determined pursuant
to Section 11(d)(i) hereof (appropriately adjusted to reflect any stock split,
stock dividend or similar transaction occurring after the date hereof)
multiplied by one hundred. If neither the Common Shares nor the Preferred Shares
are publicly held or so listed or traded, "current per share market price" shall
mean the fair value per share as determined in good faith by the Board of
Directors of the Company, whose determination shall be described in a statement
filed with the Rights Agent.

         (e) No adjustment in the Purchase Price shall be required unless such
adjustment would require an increase or decrease of at least 1% in the Purchase
Price; provided, however, that any adjustments which by reason of this Section
11(e) are not required to be made shall be carried forward and taken into
account in any subsequent adjustment. All calculations under this Section 11
shall be made to the nearest cent or to the nearest one one-hundredth of a
Preferred Share or one ten-thousandth of any other share or security as the case
may be. Notwithstanding the first sentence of this Section 11(e), any adjustment
required by this Section 11 shall be made no later than the earlier of (i) three
years from the date of the transaction which requires such adjustment or (ii)
the date of the expiration of the right to exercise any Rights.

         (f) If as a result of an adjustment made pursuant to Section 11(a)
hereof, the holder of any Right thereafter exercised shall become entitled to
receive any shares of capital stock of the Company other than Preferred Shares,
thereafter the number of such other shares so receivable upon exercise of any
Right shall be subject to adjustment from time to time in a manner and on terms
as nearly equivalent as practicable to the provisions with respect to the
Preferred Shares contained in Sections 11(a) through 11(c) hereof, inclusive,
and the provisions of Sections 7, 9, 10, 13 and 14 hereof with respect to the
Preferred Shares shall apply on like terms to any such other shares.

         (g) All Rights originally issued by the Company subsequent to any
adjustment made to the Purchase Price hereunder shall evidence the right to
purchase, at the adjusted Purchase Price, the number of one one-hundredths of a
Preferred Share purchasable from time to time hereunder upon exercise of the
Rights, all subject to further adjustment as provided herein.

         (h) Unless the Company shall have exercised its election as provided in
Section 11(i) hereof, upon each adjustment of the Purchase Price as a result of
the calculations made in Section 11(b) and Section 11(c) hereof, each Right
outstanding immediately prior to the making of such adjustment shall thereafter
evidence the right to purchase, at the adjusted Purchase Price, that number of
one one-hundredths of a Preferred Share (calculated to the nearest one
one-millionth of a Preferred Share) obtained by (i) multiplying (x) the number
of one one-hundredths of a Preferred Share covered by a Right immediately prior
to this adjustment by (y) the Purchase Price in effect immediately prior to such
adjustment of the Purchase Price and (ii) dividing the product so obtained by
the Purchase Price in effect immediately after such adjustment of the Purchase
Price.

         (i) The Company may elect on or after the date of any adjustment of the
Purchase Price to adjust the number of Rights, in substitution for any
adjustment in the number of one one-hundredths of a Preferred Share purchasable
upon the exercise of a Right. Each of the Rights outstanding after such
adjustment of the number of Rights shall be exercisable for the number of



                                      15.
<PAGE>   17

one one-hundredths of a Preferred Share for which a Right was exercisable
immediately prior to such adjustment. Each Right held of record prior to such
adjustment of the number of Rights shall become that number of Rights
(calculated to the nearest one ten-thousandth) obtained by dividing the Purchase
Price in effect immediately prior to adjustment of the Purchase Price by the
Purchase Price in effect immediately after adjustment of the Purchase Price. The
Company shall make a public announcement of its election to adjust the number of
Rights, indicating the record date for the adjustment, and, if known at the
time, the amount of the adjustment to be made. This record date may be the date
on which the Purchase Price is adjusted or any day thereafter, but, if the Right
Certificates have been issued, shall be at least 10 days later than the date of
the public announcement. If Right Certificates have been issued, upon each
adjustment of the number of Rights pursuant to this Section 11(i), the Company
shall, as promptly as practicable, cause to be distributed to holders of record
of Right Certificates on such record date Right Certificates evidencing, subject
to Section 14 hereof, the additional Rights to which such holders shall be
entitled as a result of such adjustment, or, at the option of the Company, shall
cause to be distributed to such holders of record in substitution and
replacement for the Right Certificates held by such holders prior to the date of
adjustment, and upon surrender thereof, if required by the Company, new Right
Certificates evidencing all the Rights to which such holders shall be entitled
after such adjustment. Right Certificates so to be distributed shall be issued,
executed and countersigned in the manner provided for herein and shall be
registered in the names of the holders of record of Right Certificates on the
record date specified in the public announcement.

         (j) Irrespective of any adjustment or change in the Purchase Price or
the number of one one-hundredths of a Preferred Share issuable upon the exercise
of the Rights, the Right Certificates theretofore and thereafter issued may
continue to express the Purchase Price and the number of one one-hundredths of a
Preferred Share which were expressed in the initial Right Certificates issued
hereunder.

         (k) Before taking any action that would cause an adjustment reducing
the Purchase Price below one one-hundredth of the then par value, if any, of the
Preferred Shares issuable upon exercise of the Rights, the Company shall take
any corporate action which may, in the opinion of its counsel, be necessary in
order that the Company may validly and legally issue fully paid and
nonassessable Preferred Shares at such adjusted Purchase Price.

         (l) In any case in which this Section 11 shall require that an
adjustment in the Purchase Price be made effective as of a record date for a
specified event, the Company may elect to defer until the occurrence of such
event the issuing to the holder of any Right exercised after such record date of
the Preferred Shares and other capital stock or securities of the Company, if
any, issuable upon such exercise on the basis of the Purchase Price in effect
prior to such adjustment; provided, however, that the Company shall deliver to
such holder a due bill or other appropriate instrument evidencing such holder's
right to receive such additional shares upon the occurrence of the event
requiring such adjustment.

         (m) The Company covenants and agrees that, after the Distribution Date,
it will not, except as permitted by Section 23 or Section 27 hereof, take (or
permit any Subsidiary to take) any action the purpose of which is to, or if at
the time such action is taken it is reasonably foreseeable that the effect of
such action is to, materially diminish or eliminate the benefits



                                      16.
<PAGE>   18

intended to be afforded by the Rights. Any such action taken by the Company
during any period after any Person becomes an Acquiring Person but prior to the
Distribution Date shall be null and void unless such action could be taken under
this Section 11(m) from and after the Distribution Date.

         (n) Anything in this Section 11 to the contrary notwithstanding, the
Company shall be entitled to make such reductions in the Purchase Price, in
addition to those adjustments expressly required by this Section 11, as and to
the extent that it in its sole discretion shall determine to be advisable in
order that any consolidation or subdivision of the Preferred Shares, issuance
wholly for cash of any Preferred Shares at less than the current market price,
issuance wholly for cash of Preferred Shares or securities which by their terms
are convertible into or exchangeable for Preferred Shares, dividends on
Preferred Shares payable in Preferred Shares or issuance of rights, options or
warrants referred to hereinabove in Section 11(b), hereafter made by the Company
to holders of its Preferred Shares shall not be taxable to such stockholders.

         (o) In the event that at any time after the date of this Agreement and
prior to the Distribution Date, the Company shall (i) declare or pay any
dividend on the Common Shares payable in Common Shares or (ii) effect a
subdivision, combination or consolidation of the Common Shares (by
reclassification or otherwise than by payment of dividends in Common Shares)
into a greater or lesser number of Common Shares, then in any such case (A) the
number of one one-hundredths of a Preferred Share purchasable after such event
upon proper exercise of each Right shall be determined by multiplying the number
of one one-hundredths of a Preferred Share so purchasable immediately prior to
such event by a fraction, the numerator of which is the number of Common Shares
outstanding immediately before such event and the denominator of which is the
number of Common Shares outstanding immediately after such event, and (B) each
Common Share outstanding immediately after such event shall have issued with
respect to it that number of Rights which each Common Share outstanding
immediately prior to such event had issued with respect to it. The adjustments
provided for in this Section 11(o) shall be made successively whenever such a
dividend is declared or paid or such a subdivision, combination or consolidation
is effected.

         (p) The exercise of Rights under Section 11(a)(ii) hereof shall only
result in the loss of rights under Section 11(a)(ii) hereof to the extent so
exercised and shall not otherwise affect the rights represented by the Rights
under this Agreement, including the rights represented by Section 13 hereof.

SECTION 12. CERTIFICATE OF ADJUSTED PURCHASE PRICE OR NUMBER OF SHARES. Whenever
an adjustment is made as provided in Sections 11 and 13 hereof, the Company
shall promptly (a) prepare a certificate setting forth such adjustment, and a
brief statement of the facts accounting for such adjustment, (b) file with the
Rights Agent and with each transfer agent for the Common Shares or the Preferred
Shares a copy of such certificate and (c) mail a brief summary thereof to each
holder of a Right Certificate in accordance with Section 25 hereof. The Rights
Agent shall be fully protected in relying on any such certificate and on any
adjustment therein contained and shall not be deemed to have knowledge of any
adjustment unless and until it shall have received such certificate.



                                      17.
<PAGE>   19

SECTION 13. CONSOLIDATION, MERGER OR SALE OR TRANSFER OF ASSETS OR EARNING
POWER.

         (a) In the event that, following the Shares Acquisition Date or, if a
Transaction is proposed, the Distribution Date, directly or indirectly (x) the
Company shall consolidate with, or merge with and into, any Interested
Stockholder, or if in such merger or consolidation all holders of Common Stock
are not treated alike, any other Person, (y) any Interested Person, or if in
such merger or consolidation all holders of Common Stock are not treated alike,
any other Person shall consolidate with the Company, or merge with and into the
Company, and the Company shall be the continuing or surviving corporation of
such merger (other than, in the case of either transaction described in (x) or
(y), a merger or consolidation which would result in all of the voting power
represented by the securities of the Company outstanding immediately prior
thereto continuing to represent (either by remaining outstanding or by being
converted into securities of the surviving entity) all of the voting power
represented by the securities of the Company or such surviving entity
outstanding immediately after such merger or consolidation and the holders of
such securities not having changed as a result of such merger or consolidation),
or (z) the Company shall sell, mortgage or otherwise transfer (or one or more of
its subsidiaries shall sell, mortgage or otherwise transfer), in one or more
transactions, assets or earning power aggregating more than 50% of the assets or
earning power of the Company and its subsidiaries (taken as a whole) to any
Interested Stockholder or Stockholders, or if in such transaction all holders of
Common Stock are not treated alike, any other Person, (other than the Company or
any Subsidiary of the Company in one or more transactions each of which
individually and the aggregate does not violate Section 13(d) hereof) then, and
in each such case, proper provision shall be made so that (i) each holder of a
Right, subject to Section 11(a)(ii) hereof, shall have the right to receive,
upon the exercise thereof at a price equal to the then current Purchase Price
multiplied by the number of one one-hundredths of a Preferred Share for which a
Right is then exercisable in accordance with the terms of this Agreement and in
lieu of Preferred Shares, such number of freely tradeable Common Shares of the
Principal Party (as such term is hereinafter defined), free and clear of liens,
rights of call or first refusal, encumbrances or other adverse claims, as shall
be equal to the result obtained by (A) multiplying the then current Purchase
Price by the number of one one-hundredths of a Preferred Share for which a Right
is then exercisable (without taking into account any adjustment previously made
pursuant to Section 11(a)(ii) hereof) and dividing that product by (B) 50% of
the then current per share market price of the Common Shares of such Principal
Party (determined pursuant to Section 11(d) hereof) on the date of consummation
of such consolidation, merger, sale or transfer; (ii) such Principal Party shall
thereafter be liable for, and shall assume, by virtue of such consolidation,
merger, sale or transfer, all the obligations and duties of the Company pursuant
to this Agreement; (iii) the term "Company" shall thereafter be deemed to refer
to such Principal Party, it being specifically intended that the provisions of
Section 11 hereof shall apply to such Principal Party; and (iv) such Principal
Party shall take such steps (including, but not limited to, the reservation of a
sufficient number of shares of its Common Shares in accordance with Section 9
hereof) in connection with such consummation as may be necessary to assure that
the provisions hereof shall thereafter be applicable, as nearly as reasonably
may be, in relation to its Common Shares thereafter deliverable upon the
exercise of the Rights.



                                      18.
<PAGE>   20

         (b) "Principal Party" shall mean:

               (i) in the case of any transaction described in clause (x) or (y)
of the first sentence of Section 13(a) hereof, the Person that is the issuer of
any securities into which Common Shares are converted in such merger or
consolidation, and if no securities are so issued, the Person that is the other
party to the merger or consolidation (or, if applicable, the Company, if it is
the surviving corporation); and

               (ii) in the case of any transaction described in (z) of the first
sentence of Section 13(a) hereof, the Person that is the party receiving the
greatest portion of the assets or earning power transferred pursuant to such
transaction or transactions;

provided, however, that in any case, (1) if the Common Shares of such Person are
not at such time and have not been continuously over the preceding 12-month
period registered under Section 12 of the Exchange Act, and such Person is a
direct or indirect subsidiary or Affiliate of another Person the Common Shares
of which are and have been so registered, "Principal Party" shall refer to such
other Person; (2) if such Person is a subsidiary, directly or indirectly, or
Affiliate of more than one Person, the Common Shares of two or more of which are
and have been so registered, "Principal Party" shall refer to whichever of such
Persons is the issuer of the Common Shares having the greatest aggregate market
value; and (3) if such Person is owned, directly or indirectly, by a joint
venture formed by two or more Persons that are not owned, directly or
indirectly, by the same Person, the rules set forth in (1) and (2) above shall
apply to each of the chains of ownership having an interest in such joint
venture as if such party were a "subsidiary" of both or all of such joint
venturers and the Principal Parties in each such chain shall bear the
obligations set forth in this Section 13 in the same ratio as their direct or
indirect interests in such Person bear to the total of such interests.

         (c) The Company shall not consummate any such consolidation, merger,
sale or transfer unless the Principal Party shall have a sufficient number of
authorized Common Shares that have not been issued or reserved for issuance to
permit the exercise in full of the Rights in accordance with this Section 13 and
unless prior thereto the Company and each Principal Party and each other Person
who may become a Principal Party as a result of such consolidation, merger, sale
or transfer shall have (i) executed and delivered to the Rights Agent a
supplemental agreement providing for the terms set forth in paragraphs (a) and
(b) of this Section 13 and (ii) prepared, filed and had declared and remain
effective a registration statement under the Act on the appropriate form with
respect to the Rights and the securities exercisable upon exercise of the Rights
and further providing that, as soon as practicable after the date of any
consolidation, merger, sale or transfer of assets mentioned in paragraph (a) of
this Section 13, the Principal Party at its own expense will:

               (i) cause the registration statement under the Act with respect
to the Rights and the securities purchasable upon exercise of the Rights on an
appropriate form to remain effective (with a prospectus at all times meeting the
requirements of the Act) until the Final Expiration Date;



                                      19.
<PAGE>   21

               (ii) use its best efforts to qualify or register the Rights and
the securities purchasable upon exercise of the Rights under the blue sky laws
of such jurisdictions as may be necessary or appropriate;

               (iii) list the Rights and the securities purchasable upon
exercise of the Rights on each national securities exchange on which the Common
Shares were listed prior to the consummation of the such consolidation merger,
sale or transfer of assets or on the Nasdaq National Market if the Common Shares
were listed on the Nasdaq National Market or, if the Common Shares were not
listed on a national securities exchange or the Nasdaq National Market prior to
the consummation of the such consolidation merger, sale or transfer of assets,
on a national securities exchange or the Nasdaq National Market; and

               (iv) deliver to holders of the Rights historical financial
statements for the Principal Party and each of its Affiliates which comply in
all material respects with the requirements for registration on Form 10 under
the Exchange Act.

         The provisions of this Section 13 shall similarly apply to successive
mergers or consolidations or sales or other transfers.

         (d) After the Distribution Date, the Company covenants and agrees that
it shall not (i) consolidate with, (ii) merge with or into, or (iii) sell or
transfer to, in one or more transactions, assets or earning power aggregating
more than 50% of the assets or earning power of the Company and its subsidiaries
taken as a whole, any other Person (other than a Subsidiary of the Company in a
transaction which does not violate Section 11(m) hereof), if (x) at the time of
or after such consolidation, merger or sale there are any charter or bylaw
provisions or any rights, warrants or other instruments or securities
outstanding, agreements in effect or any other action taken which would diminish
or otherwise eliminate the benefits intended to be afforded by the Rights or (y)
prior to, simultaneously with or immediately after such consolidation, merger or
sale, the stockholders of the Person who constitutes, or would constitute, the
"Principal Party" for purposes of Section 13(a) hereof shall have received a
distribution of Rights previously owned by such Person or any of its Affiliates
and Associates. The Company shall not consummate any such consolidation, merger,
sale or transfer unless prior thereto the Company and such other Person shall
have executed and delivered to the Rights Agent a supplemental agreement
evidencing compliance with this Section 13(d).

SECTION 14. FRACTIONAL RIGHTS AND FRACTIONAL SHARES.

         (a) The Company shall not be required to issue fractions of Rights or
to distribute Right Certificates which evidence fractional Rights. In lieu of
such fractional Rights, there shall be paid to the registered holders of the
Right Certificates with regard to which such fractional Rights would otherwise
be issuable, an amount in cash equal to the same fraction of the current market
value of a whole Right. For the purposes of this Section 14(a), the current
market value of a whole Right shall be the closing price of the Rights for the
Trading Day immediately prior to the date on which such fractional Rights would
have been otherwise issuable. The closing price for any day shall be the last
sale price, regular way, or, in case no such sale takes place on such day, the
average of the closing bid and asked prices, regular way, in either case as
reported in the principal consolidated transaction reporting system with respect
to securities listed or admitted to



                                      20.
<PAGE>   22

trading on the New York Stock Exchange or, if the Rights are not listed or
admitted to trading on the New York Stock Exchange, as reported in the principal
consolidated transaction reporting system with respect to securities listed on
the principal national securities exchange on which the Rights are listed or
admitted to trading or as reported on the Nasdaq National Market or, if the
Rights are not listed or admitted to trading on any national securities exchange
or reported on the Nasdaq National Market, the last quoted price or, if not so
quoted, the average of the high bid and low asked prices in the over-the-counter
market, as reported by Nasdaq or such other system then in use or, if on any
such date the Rights are not quoted by any such organization, the average of the
closing bid and asked prices as furnished by a professional market maker making
a market in the Rights selected by the Board of Directors of the Company. If on
any such date no such market maker is making a market in the Rights, the fair
value of the Rights on such date as determined in good faith by the Board of
Directors of the Company shall be used.

         (b) The Company shall not be required to issue fractions of Preferred
Shares (other than fractions which are integral multiples of one one-hundredth
of a Preferred Share) upon exercise of the Rights or to distribute certificates
which evidence fractional Preferred Shares (other than fractions which are
integral multiples of one one-hundredth of a Preferred Share). Fractions of
Preferred Shares in integral multiples of one one-hundredth of a Preferred Share
may, at the election of the Company, be evidenced by depositary receipts;
provided, however, that holders of such depositary receipts shall have all of
the designations and the powers, preferences and rights, and the qualifications,
limitations and restrictions to which they are entitled as beneficial owners of
the Preferred Shares represented by such depositary receipts. In lieu of
fractional Preferred Shares that are not integral multiples of one one-hundredth
of a Preferred Share, the Company shall pay to the registered holders of Right
Certificates at the time such Rights are exercised as herein provided an amount
in cash equal to the same fraction of the current market value of one Preferred
Share. For the purposes of this Section 14(b), the current market value of a
Preferred Share shall be the current per share market price of the Preferred
Shares (as determined pursuant to the second sentence of Section 11(d)(i)
hereof) for the Trading Day immediately prior to the date of such exercise (or,
if not publicly traded, in accordance with Section 11(d)(ii) hereof).

         (c) Following the occurrence of one of the transactions or events
specified in Section 11 hereof giving rise to the right to receive Common
Shares, capital stock equivalents (other than Preferred Shares) or other
securities upon the exercise of a Right, the Company shall not be required to
issue fractions of Common Shares or units of such Common Shares, capital stock
equivalents or other securities upon exercise of the Rights or to distribute
certificates which evidence fractional Common Shares, capital stock equivalents
or other securities. In lieu of fractional Common Shares, capital stock
equivalents or other securities, the Company shall pay to the registered holders
of Right Certificates at the time such Rights are exercised as herein provided
an amount in cash equal to the same fraction of the current market value of one
Common Share or unit of such Common Shares, capital stock equivalents or other
securities. For purposes of this Section 14(c), the current market value shall
be the current per share market price (as determined pursuant to Section
11(d)(i) hereof) for the Trading Day immediately prior to the date of such
exercise and, if such capital stock equivalent is not traded, each such capital
stock equivalent shall have the value of one one-hundredth of a Preferred Share.



                                      21.
<PAGE>   23

         (d) The holder of a Right by the acceptance of the Right expressly
waives his right to receive any fractional Rights or any fractional shares upon
exercise of a Right (except as provided above).

SECTION 15. RIGHTS OF ACTION. All rights of action in respect of this Agreement,
excepting the rights of action given to the Rights Agent under Sections 18 and
20 hereof, are vested in the respective registered holders of the Right
Certificates (and, prior to the Distribution Date, the registered holders of the
Common Shares) and any registered holder of any Right Certificate (or, prior to
the Distribution Date, of the Common Shares), without the consent of the Rights
Agent or of the holder of any other Right Certificate (or, prior to the
Distribution Date, of the Common Shares), may, in his own behalf and for his own
benefit, enforce, and may institute and maintain any suit, action or proceeding
against the Company to enforce, or otherwise act in respect of, his right to
exercise the Rights evidenced by such Right Certificate in the manner provided
in such Right Certificate and in this Agreement. Without limiting the foregoing
or any remedies available to the holders of Rights, it is specifically
acknowledged that the holders of Rights would not have an adequate remedy at law
for any breach of this Agreement and will be entitled to specific performance of
the obligations under, and injunctive relief against actual or threatened
violations of the obligations of any Person subject to, this Agreement. Holders
of Rights shall be entitled to recover the reasonable costs and expenses,
including attorneys fees, incurred by them in any action to enforce the
provisions of this Agreement.

SECTION 16. AGREEMENT OF RIGHT HOLDERS. Every holder of a Right, by accepting
the same, consents and agrees with the Company and the Rights Agent and with
every other holder of a Right that:

         (a) prior to the Distribution Date, the Rights will be transferable
only in connection with the transfer of the Common Shares;

         (b) after the Distribution Date, the Right Certificates are
transferable (subject to the provisions of this Rights Agreement) only on the
registry books of the Rights Agent if surrendered at the principal office of the
Rights Agent, duly endorsed or accompanied by a proper instrument of transfer;
and

         (c) the Company and the Rights Agent may deem and treat the person in
whose name the Right Certificate (or, prior to the Distribution Date, the
associated Common Shares certificate) is registered as the absolute owner
thereof and of the Rights evidenced thereby (notwithstanding any notations of
ownership or writing on the Right Certificates or the associated Common Shares
certificate made by anyone other than the Company or the Rights Agent) for all
purposes whatsoever, and neither the Company nor the Rights Agent shall be
affected by any notice to the contrary.

SECTION 17. RIGHT CERTIFICATE HOLDER NOT DEEMED A STOCKHOLDER. No holder, as
such, of any Right Certificate shall be entitled to vote, receive dividends or
be deemed for any purpose the holder of the Preferred Shares or any other
securities of the Company which may at any time be issuable on the exercise of
the Rights represented thereby, nor shall anything contained herein or in any
Right Certificate be construed to confer upon the holder of any Right
Certificate, as such, any of the rights of a stockholder of the Company or any
right to vote for the



                                      22.
<PAGE>   24

election of directors or upon any matter submitted to stockholders at any
meeting thereof, or to give or withhold consent to any corporate action, or to
receive notice of meetings or other actions affecting stockholders (except as
provided in Section 25 hereof), or to receive dividends or subscription rights,
or otherwise, until the Right or Rights evidenced by such Right Certificate
shall have been exercised in accordance with the provisions hereof.

SECTION 18. CONCERNING THE RIGHTS AGENT. The Company agrees to pay to the Rights
Agent reasonable compensation for all services rendered by it hereunder and,
from time to time, on demand of the Rights Agent, its reasonable expenses and
counsel fees and other disbursements incurred in the administration and
execution of this Agreement and the exercise and performance of its duties
hereunder. The Company also agrees to indemnify the Rights Agent for, and to
hold it harmless against, any loss, liability, or expense, incurred without
negligence, bad faith or willful misconduct on the part of the Rights Agent, for
anything done or omitted by the Rights Agent in connection with the acceptance
and administration of this Agreement, including the costs and expenses of
defending against any claim of liability in the premises. The indemnity provided
herein shall survive the expiration of the Rights and the termination of this
Agreement.

         The Rights Agent shall be protected and shall incur no liability for,
or in respect of any action taken, suffered or omitted by it in connection with,
its administration of this Agreement in reliance upon any Right Certificate or
certificate for the Preferred Shares or Common Shares or for other securities of
the Company, instrument of assignment or transfer, power of attorney,
endorsement, affidavit, letter, notice, direction, consent, certificate,
statement, or other paper or document believed by it to be genuine and to be
signed, executed and, where necessary, verified or acknowledged, by the proper
person or persons, or otherwise upon the advice of counsel as set forth in
Section 20 hereof. In no case will the Rights Agent be liable for special,
indirect, incidental or consequential or consequential loss or damage at any
kind whatsoever (including but not limited to lost profits), even if the Rights
Agent has been advised of such loss or damage.

SECTION 19. MERGER OR CONSOLIDATION OR CHANGE OF NAME OF RIGHTS AGENT. Any
corporation into which the Rights Agent or any successor Rights Agent may be
merged or with which it may be consolidated, or any corporation resulting from
any merger or consolidation to which the Rights Agent or any successor Rights
Agent shall be a party, or any corporation succeeding to the shareholder
services or corporate trust business of the Rights Agent or any successor Rights
Agent, shall be the successor to the Rights Agent under this Agreement without
the execution or filing of any paper or any further act on the part of any of
the parties hereto, provided that such corporation would be eligible for
appointment as a successor Rights Agent under the provisions of Section 21
hereof. In case at the time such successor Rights Agent shall succeed to the
agency created by this Agreement any of the Right Certificates shall have been
countersigned but not delivered, any such successor Rights Agent may adopt the
countersignature of the predecessor Rights Agent and deliver such Right
Certificates so countersigned; and in case at that time any of the Right
Certificates shall not have been countersigned, any successor Rights Agent may
countersign such Right Certificates either in the name of the predecessor Rights
Agent or in the name of the successor Rights Agent; and in all such cases such
Right Certificates shall have the full force provided in the Right Certificates
and in this Agreement.



                                      23.
<PAGE>   25

         In case at any time the name of the Rights Agent shall be changed and
at such time any of the Right Certificates shall have been countersigned but not
delivered, the Rights Agent may adopt the countersignature under its prior name
and deliver Right Certificates so countersigned; and in case at that time any of
the Right Certificates shall not have been countersigned, the Rights Agent may
countersign such Right Certificates either in its prior name or in its changed
name; and in all such cases such Right Certificates shall have the full force
provided in the Right Certificates and in this Agreement.

SECTION 20. DUTIES OF RIGHTS AGENT. The Rights Agent undertakes the duties and
obligations imposed by this Agreement upon the following terms and conditions,
by all of which the Company and the holders of Right Certificates, by their
acceptance thereof, shall be bound:

         (a) The Rights Agent may consult with legal counsel of its choice (who
may be legal counsel for the Company), and the opinion of such counsel shall be
full and complete authorization and protection to the Rights Agent as to any
action taken or omitted by it in good faith and in accordance with such opinion.

         (b) Whenever in the performance of its duties under this Agreement the
Rights Agent shall deem it necessary or desirable that any fact or matter be
proved or established by the Company prior to taking or suffering any action
hereunder, such fact or matter (unless other evidence in respect thereof be
herein specifically prescribed) may be deemed to be conclusively proved and
established by a certificate signed by any one of the Chairman of the Board, the
Chief Executive Officer, the President, the Chief Financial Officer, any Vice
President, the Treasurer or the Secretary of the Company and delivered to the
Rights Agent; and such certificate shall be full authorization to the Rights
Agent for any action taken or suffered in good faith by it under the provisions
of this Agreement in reliance upon such certificate.

         (c) The Rights Agent shall be liable hereunder to the Company and any
other Person only for its own negligence, bad faith or willful misconduct.

         (d) The Rights Agent shall not be liable for or by reason of any of the
statements of fact or recitals contained in this Agreement or in the Right
Certificates (except its countersignature thereof) or be required to verify the
same, but all such statements and recitals are and shall be deemed to have been
made by the Company only.

         (e) The Rights Agent shall not be under any responsibility in respect
of the validity of this Agreement or the execution and delivery hereof (except
the due execution hereof by the Rights Agent) or in respect of the validity or
execution of any Right Certificate (except its countersignature thereof); nor
shall it be responsible for any breach by the Company of any covenant or
condition contained in this Agreement or in any Right Certificate; nor shall it
be responsible for any change in the exercisability of the Rights (including the
Rights becoming void pursuant to Section 11(a)(ii) hereof) or any adjustment in
the terms of the Rights (including the manner, method or amount thereof)
provided for in Sections 3, 11, 13, 23 or 24 hereof, or the ascertaining of the
existence of facts that would require any such change or adjustment (except with
respect to the exercise of Rights evidenced by Right Certificates after receipt
of a certificate pursuant to Section 12 hereof describing such change or
adjustment); nor shall it by any act hereunder be deemed to make any
representation or warranty as to the authorization or



                                      24.
<PAGE>   26

reservation of any Preferred Shares to be issued pursuant to this Agreement or
any Right Certificate or as to whether any Preferred Shares will, when issued,
be validly authorized and issued, fully paid and nonassessable.

         (f) The Company agrees that it will perform, execute, acknowledge and
deliver or cause to be performed, executed, acknowledged and delivered all such
further and other acts, instruments and assurances as may reasonably be required
by the Rights Agent for the carrying out or performing by the Rights Agent of
the provisions of this Agreement.

         (g) The Rights Agent is hereby authorized and directed to accept
instructions with respect to the performance of its duties hereunder from any
one of the Chairman of the Board, the Chief Executive Officer, the President,
the Chief Financial Officer, any Vice President, the Secretary or the Treasurer
of the Company, and to apply to such officers for advice or instructions in
connection with its duties, and it shall not be liable for any action taken or
suffered by it in good faith in accordance with instructions of any such officer
or for any delay in acting while waiting for those instructions. Any application
by the Rights Agent for written instructions from the Company may, at the option
of the Rights Agent, set forth in writing any action proposed to be taken or
omitted by the Rights Agent with respect to its duties or obligations under this
Agreement and the date on and/or after which such action shall be taken or
omitted and the Rights Agent shall not be liable for any action taken or omitted
in accordance with a proposal included in any such application on or after the
date specified therein (which date shall not be less than three Business Days
after the date indicated in such application unless any such officer shall have
consented in writing to an earlier date) unless, prior to taking or omitting any
such action, the Rights Agent has received written instructions in response to
such application specifying the action to be taken or omitted.

         (h) The Rights Agent and any stockholder, director, officer or employee
of the Rights Agent may buy, sell or deal in any of the Rights or other
securities of the Company or become pecuniarily interested in any transaction in
which the Company may be interested, or contract with or lend money to the
Company or otherwise act as fully and freely as though it were not Rights Agent
under this Agreement. Nothing herein shall preclude the Rights Agent from acting
in any other capacity for the Company or for any other legal entity.

         (i) The Rights Agent may execute and exercise any of the rights or
powers hereby vested in it or perform any duty hereunder either itself or by or
through its attorneys or agents, and the Rights Agent shall not be answerable or
accountable for any act, default, neglect or misconduct of any such attorneys or
agents or for any loss to the Company resulting from any such act, default,
neglect or misconduct, provided reasonable care was exercised in the selection
and continued employment thereof.

         (j) No provision of this Agreement shall require the Rights Agent 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 its rights if
there shall be reasonable grounds for believing that repayment of such funds or
adequate indemnification against such risk or liability is not reasonably
assured to it.



                                      25.
<PAGE>   27

         (k) If, with respect to any Right Certificate surrendered to the Rights
Agent for exercise or transfer, the certificate attached to the form of
assignment or form of election to purchase, as the case may be, has not been
executed, the Rights Agent shall not take any further action with respect to
such requested exercise of transfer without first consulting with the Company.

SECTION 21. CHANGE OF RIGHTS AGENT. The Rights Agent or any successor Rights
Agent may resign and be discharged from its duties under this Agreement upon 30
days' notice in writing mailed to the Company and to each transfer agent for the
Common Shares or Preferred Shares by registered or certified mail, and to the
holders of the Right Certificates by first-class mail. The Company may remove
the Rights Agent or any successor Rights Agent upon 30 days' notice in writing,
mailed to the Rights Agent or successor Rights Agent, as the case may be, and to
each transfer agent for the Common Shares or Preferred Shares by registered or
certified mail, and to the holders of the Right Certificates by first-class
mail. If the Rights Agent shall resign or be removed or shall otherwise become
incapable of acting, the Company shall appoint a successor to the Rights Agent.
If the Company shall fail to make such appointment within a period of 30 days
after giving notice of such removal or after it has been notified in writing of
such resignation or incapacity by the resigning or incapacitated Rights Agent or
by the holder of a Right Certificate (who shall, with such notice, submit his
Right Certificate for inspection by the Company), then the registered holder of
any Right Certificate may apply to any court of competent jurisdiction for the
appointment of a new Rights Agent. Any successor Rights Agent, whether appointed
by the Company or by such a court, shall be either (a) a corporation business
trust or limited liability company organized and doing business under the laws
of the United States or of any other state of the United States which is
authorized under such laws to exercise corporate trust or stock transfer powers
and is subject to supervision or examination by federal or state authority and
which has at the time of its appointment as Rights Agent a combined capital and
surplus of at least $50 million or (b) a direct or indirect wholly owned
subsidiary of such an entity or its wholly-owning parent. After appointment, the
successor Rights Agent shall be vested with the same powers, rights, duties and
responsibilities as if it had been originally named as Rights Agent without
further act or deed; but the predecessor Rights Agent shall deliver and transfer
to the successor Rights Agent any property at the time held by it hereunder, and
execute and deliver any further assurance, conveyance, act or deed necessary for
the purpose. Not later than the effective date of any such appointment the
Company shall file notice thereof in writing with the predecessor Rights Agent
and each transfer agent for the Common Shares or Preferred Shares, and mail a
notice thereof in writing to the registered holders of the Right Certificates.
Failure to give any notice provided for in this Section 21, however, or any
defect therein, shall not affect the legality or validity of the resignation or
removal of the Rights Agent or the appointment of the successor Rights Agent, as
the case may be.

SECTION 22. ISSUANCE OF NEW RIGHT CERTIFICATES. Notwithstanding any of the
provisions of this Agreement or of the Rights to the contrary, the Company may,
at its option, issue new Right Certificates evidencing Rights in such form as
may be approved by its Board of Directors to reflect any adjustment or change in
the Purchase Price and the number or kind or class of shares or other securities
or property purchasable under the Right Certificates made in accordance with the
provisions of this Agreement. In addition, in connection with the issuance or
sale of Common Shares following the Distribution Date and prior to the earlier
of the Redemption Date and the Final Expiration Date, the Company (a) shall with
respect to Common



                                      26.
<PAGE>   28

Shares so issued or sold pursuant to the exercise of stock options or under any
employee plan or arrangement in existence prior to the Distribution Date, or
upon the exercise, conversion or exchange of securities, notes or debentures
issued by the Company and in existence prior to the Distribution Date, and (b)
may, in any other case, if deemed necessary or appropriate by the Board of
Directors of the Company, issue Right Certificates representing the appropriate
number of Rights in connection with such issuance or sale; provided, however,
that, (i) subject to the rights, preferences and privileges of the Series A
Non-voting Convertible Preferred Stock, par value $.001 per share, of the
Company, the Company shall not be obligated to issue any such Right Certificates
if, and to the extent that, the Company shall be advised by counsel that such
issuance would create a significant risk of material adverse tax consequences to
the Company or the Person to whom such Right Certificate would be issued, and
(ii) no Right Certificate shall be issued if, and to the extent that,
appropriate adjustment shall otherwise have been made in lieu of the issuance
thereof.

SECTION 23. REDEMPTION.

         (a) The Rights may be redeemed by action of the Board of Directors
pursuant to Section 23(b) hereof and shall not be redeemed in any other manner.

         (b)

               (i) The Board of Directors of the Company may, at its option, at
any time prior to the earlier of such time as any Person becoming an Acquiring
Person or the Final Expiration Date, redeem all but not less than all of the
then outstanding Rights at a redemption price of $0.01 per Right, appropriately
adjusted to reflect any stock split, stock dividend or similar transaction
occurring after the date hereof (such redemption price being hereinafter
referred to as the "Redemption Price"), and the Company may, at its option, pay
the Redemption Price in Common Shares (based on the "current per-share market
price," as such term is defined in Section 11(d) hereof, of the Common Shares at
the time of redemption), cash or any other form of consideration deemed
appropriate by the Board of Directors. The redemption of the Rights by the Board
of Directors may be made effective at such time, on such basis and subject to
such conditions as the Board of Directors in its sole discretion may establish.
Notwithstanding anything contained in this Agreement to the contrary, the Rights
shall not be exercisable pursuant to Section 11(a)(ii) hereof prior to the
expiration or termination of the Company's right of redemption under this
Section 23(b)(i).

               (ii) In addition, the Board of Directors of the Company may, at
its option, at any time after the time a Person becomes an Acquiring Person and
the expiration of any period during which the holder of Rights may exercise the
rights under Section 11(a)(ii) hereof but prior to any event described in clause
(x), (y) or (z) of the first sentence of Section 13 hereof, redeem all but not
less than all of the then outstanding Rights at the Redemption Price (x) in
connection with any merger, consolidation or sale or other transfer (in one
transaction or in a series of related transactions) of assets or earning power
aggregating 50% or more of the assets or earning power of the Company and its
subsidiaries (taken as a whole) in which all holders of Common Shares are
treated alike and not involving (other than as a holder of Common Shares being
treated like all other such holders) an Interested Stockholder or a Transaction
Person or (y)(A) if and for so long as the Acquiring Person is not thereafter
the Beneficial Owner of 20% or more of



                                      27.
<PAGE>   29

the then outstanding Common Shares, and (B) at the time of redemption no other
Persons are Acquiring Persons.

         (c) Immediately upon the action of the Board of Directors of the
Company ordering the redemption of the Rights pursuant to Section 23(b) hereof,
and without any further action and without any notice, the right to exercise the
Rights will terminate and the only right thereafter of the holders of Rights
shall be to receive the Redemption Price. The Company shall promptly give public
notice of any such redemption; provided, however, that the failure to give, or
any defect in, any such notice shall not affect the validity of such redemption.
Within 10 days after such action of the Board of Directors ordering the
redemption of the Rights pursuant to Section 23(b) hereof, the Company shall
mail a notice of redemption to all the holders of the then outstanding Rights at
their last addresses as they appear upon the registry books of the Rights Agent
or, prior to the Distribution Date, on the registry books of the transfer agent
for the Common Shares, provided, however, that failure to give, or any defect
in, any such notice shall not affect the validity of such redemption. Any notice
which is mailed in the manner herein provided shall be deemed given, whether or
not the holder receives the notice. Each such notice of redemption will state
the method by which the payment of the Redemption Price will be made. Neither
the Company nor any of its Affiliates or Associates may redeem, acquire or
purchase for value any Rights at any time in any manner other than that
specifically set forth in this Section 23 or in Section 24 hereof, and other
than in connection with the purchase of Common Shares prior to the Distribution
Date.

         (d) The Company may, at its option, discharge all of its obligations
with respect to any redemption of the Rights by (i) issuing a press release
announcing the manner of redemption of the Rights and (ii) mailing payment of
the Redemption Price to the registered holders of the Rights at their last
addresses as they appear on the registry books of the Rights Agent or, prior to
the Distribution Date, on the registry books of the transfer agent for the
Common Shares, and upon such action, all outstanding Right Certificates shall be
null and void without any further action by the Company.

SECTION 24. EXCHANGE.

         (a) The Board of Directors of the Company may, at its option, at any
time after any Person becomes an Acquiring Person, exchange all or part of the
then outstanding and exercisable Rights (which shall not include Rights that
have become void pursuant to the provisions of Section 11(a)(ii) hereof) for
Common Shares at an exchange ratio of one Common Share per Right, appropriately
adjusted to reflect any stock split, stock dividend or similar transaction
occurring after the date hereof (such exchange ratio being hereinafter referred
to as the "Exchange Ratio"). Notwithstanding the foregoing, the Board of
Directors shall not be empowered to effect such exchange at any time after any
Person (other than the Company, any Subsidiary of the Company, any employee
benefit plan of the Company or any such Subsidiary, or any entity holding Common
Shares for or pursuant to the terms of any such plan), together with all
Affiliates and Associates of such Person, becomes the Beneficial Owner of 50% or
more of the Common Shares then outstanding.

         (b) Immediately upon the action of the Board of Directors of the
Company ordering the exchange of any Rights pursuant to Section 24(a) hereof and
without any further action and




                                      28.
<PAGE>   30

without any notice, the right to exercise such Rights shall terminate and the
only right thereafter of a holder of such Rights shall be to receive that number
of Common Shares equal to the number of such Rights held by such holder
multiplied by the Exchange Ratio. The Company shall promptly give public notice
of any such exchange; provided, however, that the failure to give, or any defect
in, such notice shall not affect the validity of such exchange. The Company
promptly shall mail a notice of any such exchange to all of the holders of such
Rights at their last addresses as they appear upon the registry books of the
Rights Agent; provided, however, that the failure to give, or any defect in,
such notice shall not affect the validity of such exchange. Any notice which is
mailed in the manner herein provided shall be deemed given, whether or not the
holder receives the notice. Each such notice of exchange will state the method
by which the exchange of the Common Shares for Rights will be effected and, in
the event of any partial exchange, the number of Rights which will be exchanged.
Any partial exchange shall be effected pro rata based on the number of Rights
(other than Rights which have become void pursuant to the provisions of Section
11(a)(ii) hereof) held by each holder of Rights.

         (c) In lieu of issuing Common Shares in accordance with Section 24(a)
hereof, the Company may, if a majority of the Board of Directors then in office
determines that such action is necessary or appropriate and not contrary to the
interests of the holders of Rights, elect to (and, in the event that there are
not sufficient treasury shares and authorized but unissued Common Shares to
permit any exchange of the Rights in accordance with Section 24(a) hereof, the
Company shall) take all such action as may be necessary to authorize, issue or
pay, upon the exchange of the Rights, cash (including by way of a reduction of
the Purchase Price), property, Common Shares, other securities or any
combination thereof having an aggregate value equal to the value of the Common
Shares which otherwise would have been issuable pursuant to Section 24(a)
hereof, which aggregate value shall be determined by a nationally recognized
investment banking firm selected by a majority of the Board of Directors then in
office. For purposes of the preceding sentence, the value of the Common Shares
shall be determined pursuant to Section 11(d) hereof. Any election pursuant to
this Section 24(c) by the Board of Directors must be made within 60 days
following the date on which the event described in Section 11(a)(ii) hereof
shall have occurred. Following the occurrence on the event described in Section
11(a)(ii) hereof, a majority of the Board of Directors then in office may
suspend the exercisability of the Rights for a period of up to 60 days following
the date on which the event described in Section 11(a)(ii) hereof shall have
occurred to the extent that such directors have not determined whether to
exercise their rights of election under this Section 24(c). In the event of any
such suspension, the Company shall issue a public announcement stating that the
exercisability of the Rights has been temporarily suspended.

         (d) The Company shall not be required to issue fractions of Common
Shares or to distribute certificates which evidence fractional Common Shares. In
lieu of such fractional Common Shares, the Company shall pay to the registered
holders of the Right Certificates with regard to which such fractional Common
Shares would otherwise be issuable an amount in cash equal to the same fraction
of the current market value of a whole Common Share. For the purposes of this
Section 24(d), the current market value of a whole Common Share shall be the
closing price of a Common Share (as determined pursuant to the second sentence
of Section 11(d)(i) hereof) for the Trading Day immediately after the date of
the first public announcement by the Company that an exchange is to be effected
pursuant to this Section 24.



                                      29.
<PAGE>   31

         (e) The Company shall not be required to issue fractions of Preferred
Shares (other than fractions which are integral multiples of one one-hundredth
of a Preferred Share) upon exchange of the Rights or to distribute certificates
which evidence fractional Preferred Shares (other than fractions which are
integral multiples of one one-hundredth of a Preferred Share). Fractions of
Preferred Shares in integral multiples of one one-hundredth of a Preferred Share
may, at the election of the Company, be evidenced by depositary receipts;
provided, however, that holders of such depositary receipts shall have all of
the designations and the powers, preferences and rights, and the qualifications,
limitations and restrictions to which they are entitled as beneficial owners of
the Preferred Shares represented by such depositary receipts. In lieu of
fractional Preferred Shares that are not integral multiples of one one-hundredth
of a Preferred Share, the Company shall pay to the registered holders of Right
Certificates at the time such Rights are exercised as herein provided an amount
in cash equal to the same fraction of the current market value of one Preferred
Share. For the purposes of this Section 24(e), the current market value of a
Preferred Share shall be one hundred (100) times the closing price of a Common
Share (as determined pursuant to the second sentence of Section 11(d)(i) hereof)
for the Trading Day immediately after the date of the first public announcement
by the Company that an exchange is to be effected pursuant to this Section 24.

SECTION 25. NOTICE OF CERTAIN EVENTS.

         (a) In case the Company shall propose (i) to pay any dividend payable
in stock of any class to the holders of its Preferred Shares or to make any
other distribution to the holders of its Preferred Shares (other than a regular
quarterly cash dividend), (ii) to offer to the holders of its Preferred Shares
rights or warrants to subscribe for or to purchase any additional Preferred
Shares or shares of stock of any class or any other securities, rights or
options, (iii) to effect any reclassification of its Preferred Shares (other
than a reclassification involving only the subdivision of outstanding Preferred
Shares), (iv) to effect any consolidation or merger into or with, or to effect
any sale or other transfer (or to permit one or more of its Subsidiaries to
effect any sale or other transfer), in one or more transactions, of 50% or more
of the assets or earning power of the Company and its Subsidiaries (taken as a
whole), to any other Person, (v) to effect the liquidation, dissolution or
winding up of the Company, or (vi) to declare or pay any dividend on the Common
Shares payable in Common Shares or to effect a subdivision, combination or
consolidation of the Common Shares (by reclassification or otherwise than by
payment of dividends in Common Shares), then, in each such case, the Company
shall give to each holder of a Right Certificate, in accordance with Section 26
hereof, a notice of such proposed action, which shall specify the record date
for the purpose of such stock dividend, or distribution of rights or warrants,
or the date on which such reclassification, consolidation, merger, sale,
transfer, liquidation, dissolution, or winding up is to take place and the date
of participation therein by the holders of the Common Shares and/or the
Preferred Shares, if any such date is to be fixed, and such notice shall be so
given in the case of any action covered by clause (i) or (ii) above at least 10
days prior to the record date for determining holders of the Preferred Shares
for purposes of such action, and in the case of any such other action, at least
10 days prior to the date of the taking of such proposed action or the date of
participation therein by the holders of the Common Shares and/or the Preferred
Shares, whichever shall be the earlier.

         (b) In case the event set forth in Section 11(a)(ii) hereof shall
occur, then the Company shall as soon as practicable thereafter give to each
holder of a Right Certificate, in



                                      30.
<PAGE>   32

accordance with Section 26 hereof, a notice of the occurrence of such event,
which notice shall describe the event and the consequences of the event to
holders of Rights under Section 11(a)(ii) hereof.

SECTION 26. NOTICES. Notices or demands authorized by this Agreement to be given
or made by the Rights Agent or by the holder of any Right Certificate to or on
the Company shall be sufficiently given or made if sent by first-class mail,
postage prepaid, addressed (until another address is filed in writing with the
Rights Agent) as follows:

                           RIBOGENE, INC.
                           26118 RESEARCH ROAD
                           HAYWARD, CA 94545


         Subject to the provisions of Section 21 hereof, any notice or demand
authorized by this Agreement to be given or made by the Company or by the holder
of any Right Certificate to or on the Rights Agent shall be sufficiently given
or made if sent by first-class mail, postage prepaid, addressed (until another
address is filed in writing with the Company) as follows:

                           AMERICAN STOCK TRANSFER
                           6201 15TH AVENUE, THIRD FLOOR
                           BROOKLYN, NEW YORK  11219


         Notices or demands authorized by this Agreement to be given or made by
the Company or the Rights Agent to the holder of any Right Certificate shall be
sufficiently given or made if sent by first-class mail, postage prepaid,
addressed to such holder at the address of such holder as shown on the registry
books of the Company.

SECTION 27. SUPPLEMENTS AND AMENDMENTS. Prior to the Distribution Date, the
Company and the Rights Agent shall, if the Company so directs, supplement or
amend any provision of this Agreement without the approval of any holders of the
Rights. From and after the Distribution Date, the Company and the Rights Agent
shall, if the Company so directs, from time to time supplement or amend any
provision of this Agreement without the approval of any holders of Right
Certificates in order to (i) cure any ambiguity, (ii) correct or supplement any
provision contained herein which may be defective or inconsistent with any other
provisions herein, or (iii) change any other provisions with respect to the
Rights which the Company may deem necessary or desirable; provided, however,
that no such supplement or amendment shall be made which would adversely affect
the interests of the holders of Rights (other than the interests of an Acquiring
Person or its Affiliates or Associates). Any supplement or amendment adopted
during any period after any Person has become an Acquiring Person but prior to
the Distribution Date shall become null and void unless such supplement or
amendment could have been adopted by the Company from and after the Distribution
Date. Any such supplement or amendment shall be evidenced by a writing signed by
the Company and the Rights Agent. Upon delivery of a certificate from an
appropriate officer of the Company which states that the proposed supplement or
amendment is in compliance with the terms of this Section 27, the Rights Agent
shall execute such supplement or amendment unless the Rights Agent shall have
determined in good faith that



                                      31.
<PAGE>   33

such supplement or amendment would adversely affect its interest under this
Agreement. Prior to the Distribution Date, the interests of the holders of
Rights shall be deemed coincident with the interests of the holders of Common
Shares.

SECTION 28. DETERMINATION AND ACTIONS BY THE BOARD OF DIRECTORS, ETC. For all
purposes of this Agreement, any calculation of the number of Common Shares
outstanding at any particular time, including for purposes of determining the
particular percentage of such outstanding Common Shares or any other securities
of which any Person is the Beneficial Owner, shall be made in accordance with
the last sentence of Rule 13d-3(d)(1)(i) of the General Rules and Regulations
under the Exchange Act as in effect on the date of this Agreement. The Board of
Directors of the Company shall have the exclusive power and authority to
administer this Agreement and to exercise all rights and powers specifically
granted to the Board, or the Company, or as may be necessary or advisable in the
administration of this Agreement, including without limitation, the right and
power to (i) interpret the provisions of this Agreement, and (ii) make all
determinations deemed necessary or advisable for the administration of this
Agreement (including a determination to redeem or not redeem the Rights or to
amend the Agreement). All such actions, calculations, interpretations and
determinations (including, for purposes of clause (y) below, all omissions with
respect to the foregoing) which are done or made by the Board in good faith,
shall (x) be final, conclusive and binding on the Rights Agent and the holders
of the Rights, and (y) not subject the Board to any liability to the holders of
the Rights.

SECTION 29. SUCCESSORS. All the covenants and provisions of this Agreement by or
for the benefit of the Company or the Rights Agent shall bind and inure to the
benefit of their respective successors and assigns hereunder.

SECTION 30. BENEFITS OF THIS AGREEMENT. Nothing in this Agreement shall be
construed to give to any person or corporation other than the Company, the
Rights Agent and the registered holders of the Right Certificates (and, prior to
the Distribution Date, the Common Shares) any legal or equitable right, remedy
or claim under this Agreement; but this Agreement shall be for the sole and
exclusive benefit of the Company, the Rights Agent and the registered holders of
the Right Certificates (and, prior to the Distribution Date, the Common Shares).

SECTION 31. SEVERABILITY. If any term, provision, covenant or restriction of
this Agreement is held by a court of competent jurisdiction or other authority
to be invalid, void or unenforceable, the remainder of the terms, provisions,
covenants and restrictions of this Agreement shall remain in full force and
effect and shall in no way be affected, impaired or invalidated.

SECTION 32. GOVERNING LAW. This Agreement and each Right Certificate issued
hereunder shall be deemed to be a contract made under the laws of the State of
Delaware and for all purposes shall be governed by and construed in accordance
with the laws of such State applicable to contracts to be made and performed
entirely within such State.

SECTION 33. COUNTERPARTS. This Agreement may be executed in any number of
counterparts and each of such counterparts shall for all purposes be deemed to
be an original, and all such counterparts shall together constitute but one and
the same instrument.



                                      32.
<PAGE>   34

SECTION 34. DESCRIPTIVE HEADINGS. Descriptive headings of the several Sections
of this Agreement are inserted for convenience only and shall not control or
affect the meaning or construction of any of the provisions hereof.



                                      33.
<PAGE>   35



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

ATTEST:                                  RIBOGENE, INC.



/s/ Timothy E. Morris                    /s/ Charles J. Casamento
- ------------------------------           --------------------------------------
TIMOTHY E. MORRIS                        CHARLES J. CASAMENTO
Assistant Secretary                      President, Chief Executive Officer and
                                         Chairman of the Board


ATTEST:                                  AMERICAN STOCK TRANSFER &
                                         TRUST COMPANY


By: /s/ Susan Silber                     By: /s/ Herbert J. Lemmer
    --------------------------               ----------------------------------
Title: Assistant Secretary               Title: Vice President
       -----------------------                 --------------------------------





                                      34.
<PAGE>   36



                                TABLE OF CONTENTS

<TABLE>
<CAPTION>
                                                                                                                PAGE
                                                                                                                ----
<S>               <C>                                                                                           <C>
SECTION 1.        CERTAIN DEFINITIONS.............................................................................1

SECTION 2.        APPOINTMENT OF RIGHTS AGENT.....................................................................4

SECTION 3.        ISSUE OF RIGHT CERTIFICATES.....................................................................4

SECTION 4.        FORM OF RIGHT CERTIFICATES......................................................................6

SECTION 5.        COUNTERSIGNATURE AND REGISTRATION...............................................................6

SECTION 6.        TRANSFER, SPLIT UP, COMBINATION AND EXCHANGE OF RIGHT CERTIFICATES;
                  MUTILATED, DESTROYED,
                  LOST OR STOLEN RIGHT CERTIFICATES...............................................................7

SECTION 7.        EXERCISE OF RIGHTS; PURCHASE PRICE; EXPIRATION DATE OF RIGHTS...................................8

SECTION 8.        CANCELLATION AND DESTRUCTION OF RIGHT CERTIFICATES..............................................9

SECTION 9.        AVAILABILITY OF PREFERRED SHARES................................................................9

SECTION 10.       PREFERRED SHARES RECORD DATE...................................................................10

SECTION 11.       ADJUSTMENT OF PURCHASE PRICE, NUMBER OF SHARES OR NUMBER OF RIGHTS.............................11

SECTION 12.       CERTIFICATE OF ADJUSTED PURCHASE PRICE OR NUMBER OF SHARES.....................................17

SECTION 13.       CONSOLIDATION, MERGER OR SALE OR TRANSFER OF ASSETS OR EARNING POWER...........................18

SECTION 14.       FRACTIONAL RIGHTS AND FRACTIONAL SHARES........................................................20

SECTION 15.       RIGHTS OF ACTION...............................................................................22

SECTION 16.       AGREEMENT OF RIGHT HOLDERS.....................................................................22

SECTION 17.       RIGHT CERTIFICATE HOLDER NOT DEEMED A STOCKHOLDER..............................................22

SECTION 18.       CONCERNING THE RIGHTS AGENT....................................................................23

SECTION 19.       MERGER OR CONSOLIDATION OR CHANGE OF NAME OF RIGHTS AGENT......................................23

SECTION 20.       DUTIES OF RIGHTS AGENT.........................................................................24

SECTION 21.       CHANGE OF RIGHTS AGENT.........................................................................26

SECTION 22.       ISSUANCE OF NEW RIGHT CERTIFICATES.............................................................26

SECTION 23.       REDEMPTION.....................................................................................27

SECTION 24.       EXCHANGE.......................................................................................28

SECTION 25.       NOTICE OF CERTAIN EVENTS.......................................................................30

SECTION 26.       NOTICES........................................................................................31

SECTION 27.       SUPPLEMENTS AND AMENDMENTS.....................................................................31
</TABLE>



                                      i.
<PAGE>   37

                                TABLE OF CONTENTS
                                  (CONTINUED)

<TABLE>
<CAPTION>
                                                                                                                PAGE
                                                                                                                ----
<S>               <C>                                                                                           <C>
SECTION 28.       DETERMINATION AND ACTIONS BY THE BOARD OF DIRECTORS, ETC.......................................32

SECTION 29.       SUCCESSORS.....................................................................................32

SECTION 30.       BENEFITS OF THIS AGREEMENT.....................................................................32

SECTION 31.       SEVERABILITY...................................................................................32

SECTION 32.       GOVERNING LAW..................................................................................32

SECTION 33.       COUNTERPARTS...................................................................................32

SECTION 34.       DESCRIPTIVE HEADINGS...........................................................................33
</TABLE>



                                      II.


<PAGE>   1

                                                                    EXHIBIT 99.3

                                     FORM OF
                           CERTIFICATE OF DESIGNATION

                                       OF

                  SERIES B JUNIOR PARTICIPATING PREFERRED STOCK

                         (EXHIBIT A TO RIGHTS AGREEMENT)

                         (PURSUANT TO SECTION 151 OF THE
                        DELAWARE GENERAL CORPORATION LAW)


         RIBOGENE, INC., a corporation organized and existing under the General
Corporation Law of the State of Delaware (hereinafter called the "Company"),
hereby certifies that the following resolution was adopted by the Board of
Directors of the Corporation as required by Section 151 of the General
Corporation Law at a meeting duly called and held on July 1, 1999:

                           RESOLVED, that pursuant to the authority granted to
                  and vested in the Board of Directors of the Company in
                  accordance with the provisions of its Restated Certificate of
                  Incorporation, the Board of Directors hereby creates a series
                  of Preferred Stock, par value $.001 per share, of the Company
                  and hereby states the designation and number of shares, and
                  fixes the relative designations and the powers, preferences
                  and rights, and the qualifications, limitations and
                  restrictions thereof (in addition to the provisions set forth
                  in the Certificate of Incorporation of the Company, which are
                  applicable to the Preferred Stock of all classes and series),
                  as follows:

Series A Junior Participating Preferred Stock:

         SECTION 1. DESIGNATION AND AMOUNT. Three hundred thousand (300,000)
shares of Preferred Stock, $.001 par value, are designated "Series B Junior
Participating Preferred Stock" with the designations and the powers, preferences
and rights, and the qualifications, limitations and restrictions specified
herein (the "Junior Preferred Stock"). Such number of shares may be increased or
decreased by resolution of the Board of Directors; provided, that no decrease
shall reduce the number of shares of Junior Preferred Stock to a number less
than the number of shares then outstanding plus the number of shares reserved
for issuance upon the exercise of outstanding options, rights or warrants or
upon the conversion of any outstanding securities issued by the Company
convertible into Junior Preferred Stock.

         SECTION 2. DIVIDENDS AND DISTRIBUTIONS.

               (A) Subject to the rights of the holders of any shares of any
series of Preferred Stock (or any similar stock) ranking prior and superior to
the Junior Preferred Stock with respect




                                      A-1
<PAGE>   2

to dividends, the holders of shares of Junior Preferred Stock, in preference to
the holders of Common Stock, par value $.001 per share (the "Common Stock"), of
the Company, and of any other junior stock, shall be entitled to receive, when,
as and if declared by the Board of Directors out of funds legally available for
the purpose, quarterly dividends payable in cash on the first day of April,
July, October and January in each year (each such date being referred to herein
as a "Quarterly Dividend Payment Date"), commencing on the first Quarterly
Dividend Payment Date after the first issuance of a share or fraction of a share
of Junior Preferred Stock, in an amount per share (rounded to the nearest cent)
equal to the greater of (a) $l.00 or (b) subject to the provision for adjustment
hereinafter set forth, 100 times the aggregate per share amount of all cash
dividends, and 100 times the aggregate per share amount (payable in kind) of all
non-cash dividends or other distributions, other than a dividend payable in
shares of Common Stock or a subdivision of the outstanding shares of Common
Stock (by reclassification or otherwise), declared on the Common Stock since the
immediately preceding Quarterly Dividend Payment Date or, with respect to the
first Quarterly Dividend Payment Date, since the first issuance of any share or
fraction of a share of Junior Preferred Stock. In the event the Company shall at
any time declare or pay any dividend on the Common Stock payable in shares of
Common Stock, or effect a subdivision or combination or consolidation of the
outstanding shares of Common Stock (by reclassification or otherwise than by
payment of a dividend in shares of Common Stock) into a greater or lesser number
of shares of Common Stock, then in each such case the amount to which holders of
shares of Junior Preferred Stock were entitled immediately prior to such event
under clause (b) of the preceding sentence shall be adjusted by multiplying such
amount by a fraction, the numerator of which is the number of shares of Common
Stock outstanding immediately after such event and the denominator of which is
the number of shares of Common Stock that were outstanding immediately prior to
such event.

               (B) The Company shall declare a dividend or distribution on the
Junior Preferred Stock as provided in paragraph (A) of this Section immediately
after it declares a dividend or distribution on the Common Stock (other than a
dividend payable in shares of Common Stock); provided, that in the event no
dividend or distribution shall have been declared on the Common Stock during the
period between any Quarterly Dividend Payment Date and the next subsequent
Quarterly Dividend Payment Date, a dividend of $1.00 per share on the Junior
Preferred Stock shall nevertheless be payable on such subsequent Quarterly
Dividend Payment Date.

               (C) Dividends shall begin to accrue and be cumulative on
outstanding shares of Junior Preferred Stock from the Quarterly Dividend Payment
Date next preceding the date of issue of such shares, unless the date of issue
of such shares is prior to the record date for the first Quarterly Dividend
Payment Date, in which case dividends on such shares shall begin to accrue from
the date of issue of such shares, or unless the date of issue is a Quarterly
Dividend Payment Date or is a date after the record date for the determination
of holders of shares of Junior Preferred Stock entitled to receive a quarterly
dividend and before such Quarterly Dividend Payment Date, in either of which
events such dividends shall begin to accrue and be cumulative from such
Quarterly Dividend Payment Date. Accrued but unpaid dividends shall not bear
interest. Dividends paid on the shares of Junior Preferred Stock in an amount
less than the total amount of such dividends at the time accrued and payable on
such shares shall be allocated pro rata on a share-by-share basis among all such
shares at the time outstanding. The Board of Directors may fix a record date for
the determination of holders of shares of Junior Preferred




                                      A-2
<PAGE>   3

Stock entitled to receive payment of a dividend or distribution declared
thereon, which record date shall be not more than 60 days prior to the date
fixed for the payment thereof.

         SECTION 3. VOTING RIGHTS. The holders of shares of Junior Preferred
Stock shall have the following voting rights:

               (A) Subject to the provision for adjustment hereinafter set
forth, each share of Junior Preferred Stock shall entitle the holder thereof to
100 votes on all matters submitted to a vote of the stockholders of the Company.
In the event the Company shall at any time declare or pay any dividend on the
Common Stock payable in shares of Common Stock, or effect a subdivision or
combination or consolidation of the outstanding shares of Common Stock (by
reclassification or otherwise than by payment of a dividend in shares of Common
Stock) into a greater or lesser number of shares of Common Stock, then in each
such case the number of votes per share to which holders of shares of Junior
Preferred Stock were entitled immediately prior to such event shall be adjusted
by multiplying such number by a fraction, the numerator of which is the number
of shares of Common Stock outstanding immediately after such event and the
denominator of which is the number of shares of Common Stock that were
outstanding immediately prior to such event.

               (B) Except as otherwise provided herein, in any other Certificate
of Designation creating a series of Preferred Stock or any similar stock, or by
law, the holders of shares of Junior Preferred Stock and the holders of shares
of Common Stock and any other capital stock of the Company having general voting
rights shall vote together as one class on all matters submitted to a vote of
stockholders of the Company.

               (C) Except as set forth herein, or as otherwise provided by law,
holders of Junior Preferred Stock shall have no special voting rights and their
consent shall not be required (except to the extent they are entitled to vote
with holders of Common Stock as set forth herein) for taking any corporate
action.

         SECTION 4. CERTAIN RESTRICTIONS.

               (A) Whenever quarterly dividends or other dividends or
distributions payable on the Junior Preferred Stock as provided in Section 2 are
in arrears, thereafter and until all accrued and unpaid dividends and
distributions, whether or not declared, on shares of Junior Preferred Stock
outstanding shall have been paid in full, the Company shall not:

                     (i) declare or pay dividends, or make any other
distributions, on any shares of stock ranking junior (either as to dividends or
upon liquidation, dissolution or winding up) to the Junior Preferred Stock;

                     (ii) declare or pay dividends, or make any other
distributions, on any shares of stock ranking on a parity (either as to
dividends or upon liquidation, dissolution or winding up) with the Junior
Preferred Stock, except dividends paid ratably on the Junior Preferred Stock and
all such parity stock on which dividends are payable or in arrears in proportion
to the total amounts to which the holders of all such shares are then entitled;



                                      A-3
<PAGE>   4

                     (iii) redeem or purchase or otherwise acquire for
consideration shares of any stock ranking junior (either as to dividends or upon
liquidation, dissolution or winding up) to the Junior Preferred Stock, provided
that the Company may at any time redeem, purchase or otherwise acquire shares of
any such junior stock in exchange for shares of any stock of the Company ranking
junior (either as to dividends or upon dissolution, liquidation or winding up)
to the Junior Preferred Stock; or

                     (iv) redeem or purchase or otherwise acquire for
consideration any shares of Junior Preferred Stock, or any shares of stock
ranking on a parity (either as to dividends or upon liquidation, dissolution or
winding up) with the Junior Preferred Stock, except in accordance with a
purchase offer made in writing or by publication (as determined by the Board of
Directors) to all holders of such shares upon such terms as the Board of
Directors, after consideration of the respective annual dividend rates and other
relative rights and preferences of the respective series and classes, shall
determine in good faith will result in fair and equitable treatment among the
respective series or classes.

               (B) The Company shall not permit any subsidiary of the Company to
purchase or otherwise acquire for consideration any shares of stock of the
Company unless the Company could, under paragraph (A) of this Section 4,
purchase or otherwise acquire such shares at such time and in such manner.

         SECTION 5. REACQUIRED SHARES. Any shares of Junior Preferred Stock
purchased or otherwise acquired by the Company in any manner whatsoever shall be
retired and cancelled promptly after the acquisition thereof. All such shares
shall upon their cancellation become authorized but unissued shares of Preferred
Stock and may be reissued as part of a new series of Preferred Stock subject to
the conditions and restrictions on issuance set forth herein, in the Certificate
of Incorporation, or in any other Certificate of Designation creating a series
of Preferred Stock or any similar stock or as otherwise required by law.

         SECTION 6. LIQUIDATION, DISSOLUTION OR WINDING UP. Upon any
liquidation, dissolution or winding up of the Company, no distribution shall be
made (1) to the holders of shares of stock ranking junior (either as to
dividends or upon liquidation, dissolution or winding up) to the Junior
Preferred Stock unless, prior thereto, the holders of shares of Junior Preferred
Stock shall have received $100 per share, plus an amount equal to accrued and
unpaid dividends and distributions thereon, whether or not declared, to the date
of such payment, provided that the holders of shares of Junior Preferred Stock
shall be entitled to receive an aggregate amount per share, subject to the
provision for adjustment hereinafter set forth, equal to 100 times the aggregate
amount to be distributed per share to holders of shares of Common Stock, or (2)
to the holders of shares of stock ranking on a parity (either as to dividends or
upon liquidation, dissolution or winding up) with the Junior Preferred Stock,
except distributions made ratably on the Junior Preferred Stock and all such
parity stock in proportion to the total amounts to which the holders of all such
shares are entitled upon such liquidation, dissolution or winding up. In the
event the Company shall at any time declare or pay any dividend on the Common
Stock payable in shares of Common Stock, or effect a subdivision or combination
or consolidation of the outstanding shares of Common Stock (by reclassification
or otherwise than by payment of a dividend in shares of Common Stock) into a
greater or lesser number of shares of Common Stock, then in each such case the
aggregate amount to which holders of shares of Junior



                                      A-4
<PAGE>   5

Preferred Stock were entitled immediately prior to such event under the proviso
in clause (1) of the preceding sentence shall be adjusted by multiplying such
amount by a fraction the numerator of which is the number of shares of Common
Stock outstanding immediately after such event and the denominator of which is
the number of shares of Common Stock that were outstanding immediately prior to
such event.

         SECTION 7. CONSOLIDATION, MERGER, ETC. In case the Company shall enter
into any consolidation, merger, combination or other transaction in which the
shares of Common Stock are exchanged for or changed into other stock or
securities, cash and/or any other property, then in any such case each share of
Junior Preferred Stock shall at the same time be similarly exchanged or changed
into an amount per share, subject to the provision for adjustment hereinafter
set forth, equal to 100 times the aggregate amount of stock, securities, cash
and/or any other property (payable in kind), as the case may be, into which or
for which each share of Common Stock is changed or exchanged. In the event the
Company shall at any time declare or pay any dividend on the Common Stock
payable in shares of Common Stock, or effect a subdivision or combination or
consolidation of the outstanding shares of Common Stock (by reclassification or
otherwise than by payment of a dividend in shares of Common Stock) into a
greater or lesser number of shares of Common Stock, then in each such case the
amount set forth in the preceding sentence with respect to the exchange or
change of shares of Junior Preferred Stock shall be adjusted by multiplying such
amount by a fraction, the numerator of which is the number of shares of Common
Stock outstanding immediately after such event and the denominator of which is
the number of shares of Common Stock that were outstanding immediately prior to
such event.

         SECTION 8. NO REDEMPTION. The shares of Junior Preferred Stock shall
not be redeemable.

         SECTION 9. RANK. The Junior Preferred Stock shall rank, with respect to
the payment of dividends and the distribution of assets, junior to all series of
any other class of the Company's Preferred Stock.

         SECTION 10. AMENDMENT. The Restated Certificate of Incorporation of the
Company shall not be amended in any manner which would materially alter or
change the powers, preferences or special rights of the Junior Preferred Stock
so as to affect them adversely without the affirmative vote of the holders of at
least two-thirds of the outstanding shares of Junior Preferred Stock, voting
together as a single class.




                                      A-5
<PAGE>   6


         IN WITNESS WHEREOF, the undersigned have executed this certificate as
of July 1, 1999.

                             /s/ Charles J. Casamento
                             ------------------------------------------
                             CHARLES J. CASAMENTO
                             CHAIRMAN, PRESIDENT AND
                             CHIEF EXECUTIVE OFFICER


                             /s/ Timothy E. Morris
                             ------------------------------------------
                             TIMOTHY E. MORRIS
                             VICE PRESIDENT, FINANCE AND ADMINISTRATION,
                             CHIEF FINANCIAL OFFICER AND
                             ASSISTANT SECRETARY



                                      A-6

<PAGE>   1

                                                                    EXHIBIT 99.4

                            FORM OF RIGHT CERTIFICATE
                         (EXHIBIT B TO RIGHTS AGREEMENT)


CERTIFICATE NO. R-                                                _____ RIGHTS


    NOT EXERCISABLE AFTER JUNE 30, 2009 OR EARLIER IF REDEMPTION OR
    EXCHANGE OCCURS. THE RIGHTS ARE SUBJECT TO REDEMPTION AT $.01 PER RIGHT
    AND TO EXCHANGE ON THE TERMS SET FORTH IN THE RIGHTS AGREEMENT.


                                RIGHT CERTIFICATE

                                 RIBOGENE, INC.


         This certifies that ___________________ or registered assigns, is the
registered owner of the number of Rights set forth above, each of which entitles
the owner thereof, subject to the terms, provisions and conditions of the Rights
Agreement, dated as of July 1, 1999 (the "Rights Agreement"), between RiboGene,
Inc., a Delaware corporation (the "Company"), and American Stock Transfer (the
"Rights Agent"), to purchase from the Company at any time after the Distribution
Date (as such term is defined in the Rights Agreement) and prior to 5 p.m.,
eastern Standard Time, on May 16, 2009 at the office of the Rights Agent
designated for such purpose, or at the office of its successor as Rights Agent,
one one-hundredth of a fully paid non-assessable share of Series A Junior
Participating Preferred Stock, par value $.001 per share (the "Preferred
Shares"), of the Company, at a purchase price of $25.00 per one one-hundredth of
a Preferred Share (the "Purchase Price"), upon presentation and surrender of
this Right Certificate with the Form of Election to Purchase duly executed. The
number of Rights evidenced by this Right Certificate (and the number of one
one-hundredths of a Preferred Share which may be purchased upon exercise hereof)
set forth above, and the Purchase Price set forth above, are the number and
Purchase Price as of _______________, ____, based on the Preferred Shares as
constituted at such date.

         From and after the time any Person becomes an Acquiring Person, (as
such terms are defined in the Rights Agreement), if the Rights evidenced by this
Right Certificate are beneficially owned by (i) an Acquiring Person or an
Affiliate or Associate of any such Acquiring Person (as such terms are defined
in the Rights Agreement), (ii) a transferee of any such Acquiring Person,
Associate or Affiliate who becomes a transferee after the Acquiring Person
becomes such, or (iii) under certain circumstances specified in the Rights
Agreement, a transferee of any such Acquiring Person, Associate or Affiliate who
becomes a transferee prior to or concurrently with the Acquiring Person becoming
such, such Rights shall become null and void without any further action and no
holder hereof shall have any right with respect to such Rights from and after
the time any Person becomes an Acquiring Person.



                                      B-1
<PAGE>   2

         As provided in the Rights Agreement, the Purchase Price and the number
of one one-hundredths of a Preferred Share which may be purchased upon the
exercise of the Rights evidenced by this Right Certificate are subject to
modification and adjustment upon the happening of certain events.

         This Right Certificate is subject to all of the terms, provisions and
conditions of the Rights Agreement, as amended from time to time, which terms,
provisions and conditions are hereby incorporated herein by reference and made a
part hereof and to which Rights Agreement reference is hereby made for a full
description of the rights, limitations of rights, obligations, duties and
immunities hereunder of the Rights Agent, the Company and the holders of the
Right Certificates. Copies of the Rights Agreement are on file at the principal
executive offices of the Company and the above-mentioned offices of the Rights
Agent.

         This Right Certificate, with or without other Right Certificates, upon
surrender at the office of the Rights Agent designated for such purpose, may be
exchanged for another Right Certificate or Right Certificates of like tenor and
date evidencing Rights entitling the holder to purchase a like aggregate number
of Preferred Shares as the Rights evidenced by the Right Certificate or Right
Certificates surrendered shall have entitled such holder to purchase. If this
Right Certificate shall be exercised in part, the holder shall be entitled to
receive upon surrender hereof another Right Certificate or Right Certificates
for the number of whole Rights not exercised.

         Subject to the provisions of the Rights Agreement, the Rights evidenced
by this Certificate (i) may be redeemed by the Company at a redemption price of
$.01 per Right or (ii) may be exchanged in whole or in part for shares of the
Company's Common Stock, par value $.001 per share, or, upon circumstances set
forth in the Rights Agreement, cash, property or other securities of the
Company, including fractions of a share of Preferred Stock.

         No fractional Preferred Shares will be issued upon the exercise of any
Right or Rights evidenced hereby (other than fractions which are integral
multiples of one one-hundredth of a Preferred Share, which may, at the election
of the Company, be evidenced by depositary receipts) but in lieu thereof a cash
payment will be made, as provided in the Rights Agreement.

         No holder of this Right Certificate shall be entitled to vote or
receive dividends or be deemed for any purpose the holder of the Preferred
Shares or of any other securities of the Company which may at any time be
issuable on the exercise hereof, nor shall anything contained in the Rights
Agreement or herein be construed to confer upon the holder hereof, as such, any
of the rights of a stockholder of the Company or any right to vote for the
election of directors or upon any matter submitted to stockholders at any
meeting thereof, or to give or withhold consent to any corporate action, or to
receive notice of meetings or other actions affecting stockholders (except as
provided in the Rights Agreement), or to receive dividends or subscription
rights, or otherwise, until the Right or Rights evidenced by this Right
Certificate shall have been exercised as provided in the Rights Agreement.

         This Right Certificate shall not be valid or obligatory for any purpose
until it shall have been countersigned by the Rights Agent.



                                      B-2
<PAGE>   3

         WITNESS the facsimile signature of the proper officers of the Company
and its corporate seal. Dated as of __________.


ATTEST:                                  RIBOGENE, INC.


- ---------------------------------        --------------------------------------
TIMOTHY E. MORRIS                        CHARLES J. CASAMENTO
ASSISTANT SECRETARY                      PRESIDENT, CHIEF EXECUTIVE OFFICER AND
                                         CHAIRMAN OF THE BOARD

COUNTERSIGNED:



- ---------------------------------
as Rights Agent


By:
   ------------------------------
   [AUTHORIZED SIGNATURE]



                                      B-3
<PAGE>   4



                    FORM OF REVERSE SIDE OF RIGHT CERTIFICATE


                               FORM OF ASSIGNMENT


                (TO BE EXECUTED BY THE REGISTERED HOLDER IF SUCH
               HOLDER DESIRES TO TRANSFER THE RIGHT CERTIFICATE.)


         FOR VALUE RECEIVED ______________________________________ hereby sells,
assigns and transfers unto

_______________________________________________________________________________
                  (Please print name and address of transferee)

______________________________________________________________ this Right
Certificate, together with all right, title and interest therein, and does
hereby irrevocably constitute and appoint ________________________ Attorney, to
transfer the within Right Certificate on the books of the within-named Company,
with full power of substitution.


Dated:  ____________________


                                                 ___________________________
                                                 Signature




            FORM OF REVERSE SIDE OF RIGHT CERTIFICATE -- CONTINUED

                                      B-4
<PAGE>   5


SIGNATURE GUARANTEED:


         Signatures must be guaranteed by an "eligible guarantor institution" as
defined in Rule 17Ad-15 promulgated under the Securities Exchange Act of 1934,
as amended.

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

         The undersigned hereby certifies that (1) the Rights evidenced by this
Right Certificate are not being sold, assigned or transferred by or on behalf of
a Person who is or was an Acquiring Person, an Interested Stockholder or an
Affiliate or Associate thereof (as such terms are defined in the Rights
Agreement); and (2) after due inquiry and to the best of the knowledge of the
undersigned, the undersigned did not acquire the Rights evidenced by this Right
Certificate from any Person who is or was an Acquiring Person, an Interested
Stockholder, or an Affiliate or Associate thereof.



                                                 ___________________________
                                                 Signature




                                      B-5
<PAGE>   6


                          FORM OF ELECTION TO PURCHASE

                  (TO BE EXECUTED IF HOLDER DESIRES TO EXERCISE
                  RIGHTS REPRESENTED BY THE RIGHT CERTIFICATE.)


To    American Stock Transfer & Trust Company:

         The undersigned hereby irrevocably elects to exercise _________________
Rights represented by this Right Certificate to purchase the Preferred Shares
issuable upon the exercise of such Rights and requests that certificates for
such Preferred Shares be issued in the name of:

Please insert social security
or other identifying number: ______________


_______________________________________________________________________________
                         (Please print name and address)

_______________________________________________________________________________



If such number of Rights shall not be all the Rights evidenced by this Right
Certificate, a new Right Certificate for the balance remaining of such Rights
shall be registered in the name of and delivered to:

Please insert social security
or other identifying number: ______________


_______________________________________________________________________________
                         (Please print name and address)

_______________________________________________________________________________



Dated:  _________________


                                                 ___________________________
                                                 Signature



FORM OF REVERSE SIDE OF RIGHT CERTIFICATE -- CONTINUED

                                       B-6

<PAGE>   7

SIGNATURE GUARANTEED:


         Signatures must be guaranteed by an "eligible guarantor institution" as
defined in Rule 17Ad-15 promulgated under the Securities Exchange Act of 1934,
as amended.


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

         The undersigned hereby certifies that (1) the Rights evidenced by this
Right Certificate are not beneficially owned by nor are they being exercised on
behalf of an Acquiring Person, an Interested Stockholder or an Affiliate or
Associate thereof (as such terms are defined in the Rights Agreement); and (2)
after due inquiry and to the best of the knowledge of the undersigned, the
undersigned did not acquire the Rights evidenced by this Right Certificate from
any Person who is or was an Acquiring Person, an Interested Stockholder, or an
Affiliate or Associate thereof.


                                                 ___________________________
                                                 Signature


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

                                     NOTICE

         The signature in the Form of Assignment or Form of Election to
Purchase, as the case may be, must conform to the name as written upon the face
of this Right Certificate in every particular, without alteration or enlargement
or any change whatsoever.

         In the event the certification set forth above in the Form of
Assignment or the Form of Election to Purchase, as the case may be, is not
completed, the Company and the Rights Agent will deem the beneficial owner of
the Rights evidenced by this Right Certificate to be an Acquiring Person or an
Affiliate or Associate thereof (as defined in the Rights Agreement) and such
Assignment or Election to Purchase will not be honored.


                                      B-7



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