Abstract
The SAS2 gene is involved in transcriptional silencing in Saccharomyces cerevisiae. Based on its primary sequence, the Sas2 protein is predicted to be a member of the MYST family of histone acetyltransferases (HATs). Sas2 forms a complex with Sas4 and Sas5, which are required for its silencing function. Here we show that recombinant Sas2 has HAT activity that absolutely requires Sas4 and is stimulated by Sas5. The recombinant SAS complex acetylates H4 lysine 16 and H3 lysine 14. Furthermore, a purified SAS complex from yeast shows similar activity and specificity. In contrast to other MYST HATs, neither the recombinant nor the native SAS complex acetylated nucleosomal histones under conditions that were optimum for acetylating free histones. Finally, although the SAS subunits interact genetically and physically with Asf1, a histone deposition factor, association of H3 and H4 with Asf1 blocks their acetylation by the SAS complex, raising the possibility that the SAS HAT complex may acetylate free histones prior to their deposition onto DNA by Asf1 or CAF-I.
Highlights
The SAS2 gene is involved in transcriptional silencing in Saccharomyces cerevisiae
The SAS2 gene was identified in two screens for genes involved in transcriptional silencing [3, 4]. sas2 mutants are defective in silencing at telomeres, and at HML in a ⌬sir1 background, but display improved silencing at a mutated HMR locus [3, 4] and at rDNA [5]
When the soluble fraction was purified using nickel-affinity chromatography by virtue of the His tag on Sas2, substantial amounts of Sas4 and Sas5 coeluted with Sas2, indicating that the proteins formed a complex in E. coli (Fig. 1B)
Summary
Vol 278, No 19, Issue of May 9, pp. 16887–16892, 2003 Printed in U.S.A. Sas and Sas Are Required for the Histone Acetyltransferase Activity of Sas in the SAS Complex*. Cac is a subunit of the yeast CAF-I complex [12] Both Asf and CAF-I bind to histones H3 and H4 and are suggested to function in non-overlapping pathways for histone deposition and chromatin assembly [13,14,15,16,17,18]. Cac mutations cause silencing defects at HML and HMR that are only partially epistatic with sas mutations [5]. Together, these data suggest that the interactions among the SAS complex, CAF-I, and Asf may be complex and locus-specific. In this study we show that co-expression of Sas, Sas, and Sas in Escherichia coli leads to formation of a stable SAS
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
