Histone Deacetylases Associated with the mSin3 Corepressor Mediate Mad Transcriptional Repression

Transcriptional repression by Mad–Max heterodimers requires interaction of Mad with the corepressors mSin3A/B. Sin3p, the S. cerevisiae homolog of mSin3, functions in the same pathway as Rpd3p, a protein related to two recently identified mammalian histone deacetylases, HDAC1 and HDAC2. Here, we demonstrate that mSin3A and HDAC1/2 are associated in vivo. HDAC2 binding requires a conserved region of mSin3A capable of mediating transcriptional repression. In addition, Mad1 forms a complex with mSin3 and HDAC2 that contains histone deacetylase activity. Trichostatin A, an inhibitor of histone deacetylases, abolishes Mad repression. We propose that Mad–Max functions by recruiting the mSin3–HDAC corepressor complex that deacetylates nucleosomal histones, producing alterations in chromatin structure that block transcription.