Under normal circumstances, the fund invests at least 80% of its net assets (plus any borrowings for investment purposes) in securities issued, backed or otherwise guaranteed by the U.S. government, or its agencies or instrumentalities. It may invest in MBS, including collateralized mortgage obligations, issued, backed or otherwise guaranteed by the U.S. government or its agencies or instrumentalities or privately issued but collateralized by fixed or adjustable rate mortgages that are insured, guaranteed or otherwise backed by the U.S. government, or its agencies or instrumentalities.