Normally, the fund invests at least 80% of its net assets in debt securities issued or guaranteed by the U.S. government, its agencies and instrumentalities, investment grade debt securities (including convertible debt) of corporate or other issuers and cash, cash equivalents and other short-term holdings. The fund may invest a substantial portion of its assets in mortgage-related securities, including commercial mortgage-backed securities, collateralized mortgage obligations, credit risk transfer securities, and “sub-prime” mortgages, and asset-backed securities.