TRANSCRIPTIONAL REPRESSION BY UME6 INVOLVES DEACETYLATION OF LYSINE-5OF HISTONE H4 BY RPD3

The histone deacetylase RPD3 can be targeted to certain genes through its interaction with DNA-binding regulatory proteins. RPD3 can then re press gene transcription(1-6). In the yeast Saccharomyces cerevisiae, association of RPD3 with the transcriptional repressors SIN3 and UME6 results in repression of reporter genes containing the UME6-binding si te(3). RPD3 can deacetylate all histone HS acetylation sites in cell e xtracts(7). However, it is unknown how H4 proteins located at genes ne ar UME6-binding sites are affected, nor whether the effect of RPD3 is localized to the promoter regions. Here we study the mechanism by whic h RPD3 represses gene activity by examining the acetylation state of h istone proteins at UME6-regulated genes. We used antibodies specific f or individual acetylation sites in H4 to immunoprecipitate chromatin f ragments. A deletion of RPD3 or SIN3, but not of the related histone-d eacetylase gene HDA1, results in increased acetylation of the lysine 5 residue of H4 in the promoters of the UME6-regulated INO1 (ref. 8), I ME2! (ref. 3) and SPO13 (ref. 9) genes. As increased acetylation of th is residue is not merely a consequence of gene transcription, acetylat ion of this site may be essential for regulating gene activity.