<PAGE>
SUPPLEMENT DATED MARCH 23, 1998
TO PROSPECTUS DATED JANUARY 30, 1998
OF
WM PRIME INCOME FUND
FORMERLY KNOWN AS
SIERRA PRIME INCOME FUND
P.O. BOX 5118
WESTBORO, MASSACHUSETTS 01581-5118
The Prospectus, dated January 30, 1998, as supplemented to date, for the Class A
Common Shares of the Sierra Prime Income Fund (the "Fund") is hereby amended and
supplemented as follows:
The name of the Fund is the WM Prime Income Fund.
WM Advisors, Inc., formerly known as Composite Research & Management Co. ("WM
Advisors") is now the investment advisor for the Fund. Van Kampen is still the
sub-advisor for the Fund. The individual with primary responsibility for the
day-to-day management of the Fund is unchanged. WM Shareholder Services, Inc.,
formerly known as Murphey Favre Securities Services, Inc., an affiliate of WM
Advisors, is now the transfer agent and administrator for the Fund. WM Funds
Distributor, Inc., formerly known as Composite Funds Distributor, Inc., is now
the Distributor of the Fund.
PLEASE RETAIN THIS SUPPLEMENT FOR FUTURE REFERENCE
