Using a reconstituted chromatin transcription system, we have studied the initiation and elongation phases of transcription. We have defined four different families of factors that affect transcription on chromatin templates. One family requires ATP hydrolysis and functions in an activator-dependent manner to remodel chromatin structure at the promoter to allow the formation of transcription initiation complexes. One of the remaining families acetylates the tails of histone polypeptides, and the other deacetylates histone polypeptides. Polymerases that initiate transcription on remodeled chromatin templates encounter a block to transcription proximal to the promoter.
Histone acetylation plays a key role in the regulation of eukaryotic gene expression.
Histone acetylation and deacetylation are catalyzed by distinct multisubunit complexes that mediate, respectively, activation and repression of transcription. We found that a SAP30 homologue in yeast is functionally related to Sin3 and the histone deacetylase Rpd3. These results define SAP30 as a component of a histone deacetylase complex conserved among eukaryotic organisms. The histone deacetylase activity of the core complex is severely compromised. The MTA2 subunit of the NuRD 7omplex modulates the enzymatic activity of the histone deacetylase core complex.