The Drosophila sex determination gene snf encodes a nuclear protein with sequence and functional similarity to the mammalian U1A snRNP protein.

Atlternative splicing controls the expression of many genes, including the Drosopbila sex determination gene Sex-lethal. Previous studies have suggested that snf plays a role in regulating Sex-lethal splicing. Here, we demonstrate that snf is an integral component of the machinery required for splice site recognition. We have cloned snf and found that it has sequence homology to the mammalian U1A and U2B'' snRNA proteins. Moreover, we establish that snf encodes a Drosophila protein shown previously to have functional similarity to U1A. Finally, with the isolation and analysis of a null mutation, we demonstrate that snf is an essential gene