HISTONE DEACETYLASES AND SAP18, A NOVEL POLYPEPTIDE, ARE COMPONENTS OF A HUMAN SIN3 COMPLEX

An important event in gene expression is the covalent modification of histone proteins. We have found that the mammalian transcriptional rep ressor Sin3 (mSin3) exists in a complex with histone deacetylases HDAC 1 and HDAC2. Consistent with the observation that mSin3-mediated repre ssion of transcription involves the modification of histone polypeptid es, we found that the mSin3-containing complex includes polypeptides t hat tether the mSin3 complex to core histone proteins. In addition, tw o novel mSin3-associated polypeptides, SAP18 and SAP30, were identifie d. We isolated a cDNA encoding human SAP18 and found that SAP18 is a c omponent of an mSin3-containing complex in vivo. Moreover, we demonstr ate a direct interaction between SAP18 and mSin3. SAP18 represses tran scription in vivo when tethered to the promoter, consistent with the a bility of SAP18 to interact with mSin3.