IDENTIFICATION OF THE SACCHAROMYCES-CEREVISIAE GENES STB1-STB5 ENCODING SIN3P BINDING-PROTEINS

The yeast SIN3 gene functions as a transcriptional repressor, despite the fact that Sin3p does not bind DNA directly. We have conducted a tw o-hybrid screen to look for proteins that interact with Sin3p, using t he PAH2 domain of Sin3p as bait. Five new genes, STB1-STB5 were identi fied, as well as the STB6 gene, which is similar to STB2. STB1, STB2, STB3, and STB6 are novel genes, and STB4 and STB5 encode C6 zinc clust er DNA-binding proteins. None of these genes is essential for viabilit y, and several of these genes may encode transcriptional activators. S everal special problems were encountered in using a transcriptional re pressor in a two-hybrid screen. For example, the STB genes will intera ct with a LexA-Sin3(PAH2) fusion protein containing a region of Sin3p, but a LexA-Sin3p fusion protein containing full-length Sin3p, along w ith a STB clone, does not produce two-hybrid activation of a transcrip tional reporter. In addition, a sin3 mutation reduces the transcriptio nal activation by two-hybrid partners, suggesting that a sin3 mutation reduces the transcriptional efficiency of the Gal14p and VP16 activat ion domains. We have shown previously that Sin3p is part of a large mu ltiprotein complex, and we show here that Stb1p and Stb2p are present in this complex.