The yeast SAS (something about silencing) protein complex contains a MYST-type putative acetyltransferase and functions with chromatin assembly factor ASF1

It is well established that acetylation of histone and nonhistone proteins is intimately linked to transcriptional activation. However, loss of acetyl transferase activity has also been shown to cause silencing defects, implic ating acetylation in gene silencing. The something about silencing (Sas) 2 protein of Saccharomyces cerevisiae, a member of the MYST (MOZ, Ybf2/Sas3, Sas2, and TIP60) acetyltransferase family, promotes silencing at HML and te lomeres. Here we identify a similar to 450-kD SAS complex containing Sas2p, Sas4p, and the tf2f-related Sas5 protein. Mutations in the conserved acety l-CoA binding motif of Sas2p are shown to disrupt the ability of Sas2p to m ediate the silencing at HML and telomeres, providing evidence for an import ant role for the acetyltransferase activity of the SAS complex in silencing . Furthermore, the SAS complex is found to interact with chromatin assembly factor Asf1p, and asf1 mutants show silencing defects similar to mutants i n the SAS complex. Thus, ASF1-dependent chromatin assembly may mediate the role of the SAS complex in silencing.