| Description |
The SIN3 gene is a negative regulator of transcription of many genes in S. cerevisiae; however, Sin3p does not bind DNA. It has been proposed that Sin3p associates with DNA-binding proteins. To examine how SinSp represses transcription, I have identified genetically Sin3p protein binding partners and characterized biochemically the SinSp repression complex. To identify these interacting proteins, I used the two hybrid screen in yeast with the PAH2 domain of Sin3p. I have identified five new yeast proteins that interact with PAH2, encoded by the STB genes. The STB genes have been cloned and characterized. Stb4p and Stb5p contain classical C6 zinc cluster domains, supporting the hypothesis that SinSp interacts with DNA-binding proteins. Genetic analysis of the STB genes has not demonstrated a convincing role in SIN3 transcriptional regulation. The Sin3p complex has been characterized by gel filtration and glycerol gradient sedimentation. SinSp is present in a greater than 2 million dalton complex, and Sin3p associates biochemically with Stblp, Stb2p, and RpdSp. Ten polypeptides were identified that associate with Sin3p in the greater than 2 million dalton complex. Recently it has been determined that the mouse bHLH-Zip protein, Mad, interacts with a mouse homolog of yeast SinSp, and it has been suggested that this interaction is important for Mad function. Mad also interacts with ySinSp through the PAH2 region. Endogenous ySinSp also associates with the Mad-Max complex in yeast to repress transcription. The role of Sin3p and Rpd3p in transcriptional repression and chromatin modification is discussed. |
