SEX-LETHAL INTERACTS WITH SPLICING FACTORS IN-VITRO AND IN-VIVO

The Drosophila sex determination gene Sex-lethal controls its own expr ession and the expression of downstream target genes such as transform er by regulating RNA splicing. Genetic and molecular studies have esta blished that Sri requires the product of another gene, snf, to autoreg ulate the splicing of its own transcripts. snf has recently been shown to encode a Drosophila U1 and U2 small nuclear ribonucleoprotein part icle protein, In the work reported here, we demonstrate that the Sri a nd Snf proteins can interact directly in vitro and that these two prot eins are part of an RNase-sensitive complex in vivo which can be immun oprecipitated with the Sri antibody. Unlike bulk Snf protein, which se diments slowly in sucrose gradients, the Snf protein associated with S ri is in a large, rapidly sedimenting complex. Detailed characterizati on of the Sxl-Snf complexes from cross-linked extracts indicates that these complexes contain additional small nuclear ribonucleoprotein par ticle proteins and the U1 and U2 small nuclear RNAs. Finally, consiste nt with the RNase sensitivity of the Sxl-Snf complexes, Sri transcript s can also be immunoprecipitated by Sri antibodies. On the basis of th e physical interactions between Sri and Snf, we present a model for Sr i splicing regulation. This model helps explain how the Sri protein is able to promote the sex-specific splicing of Sri transcripts, utilizi ng target sequences that are distant from the regulated splice sites.