SAS4 is a family of largely fungal silencing regulators. This silencing is mediated by chromatin. SAS4 specifically silences the yeast mating-type genes HML and HMR [1]. SAS4 is found to be one subunit of a complex, the SAS complex, that interacts with chromatin assembly factor Asf1p, and asf1 mutants show silencing defects similar to mutants in the SAS complex. Thus, ASF1-dependent chromatin-assembly may mediate the role of the SAS complex in silencing [2]. Co-expression of Sas2, SAS4, and Sas5 in Escherichia coli leads to formation of a stable SAS complex that acetylates histones. SAS4 is essential for the acetyltransferase activity of Sas2, and Sas5 is also important [3].

1: Identification of SAS4 and SAS5, two genes that regulate silencing in Saccharomyces cerevisiae. Xu EY, Kim S, Replogle K, Rine J, Rivier DH; Genetics. 1999;153:13-23. PMID:10471696

2: The yeast SAS (something about silencing) protein complex contains a MYST-type putative acetyltransferase and functions with chromatin assembly factor ASF1. Osada S, Sutton A, Muster N, Brown CE, Yates JR 3rd, Sternglanz R, Workman JL; Genes Dev. 2001;15:3155-3168. PMID:11731479

3: Sas4 and Sas5 are required for the histone acetyltransferase activity of Sas2 in the SAS complex. Sutton A, Shia WJ, Band D, Kaufman PD, Osada S, Workman JL, Sternglanz R; J Biol Chem. 2003;278:16887-16892. PMID:12626510