Promoter regulation by distinct mechanisms of functional interplay between lysine acetylase Rtt109 and histone chaperone Asf1.

The promoter activity of yeast genes can depend on lysine 56 (K56) acetylation of histone H3. This modification of H3 is performed by lysine acetylase Rtt109 acting in concert with histone chaperone Asf1. We have examined the contributions of Rtt109, Asf1, and H3 K56 acetylation to nutrient regulation of a well-studied metabolic gene, ARG1. As expected, Rtt109, Asf1, and H3 K56 acetylation are required for maximal transcription of ARG1 under inducing conditions. However, Rtt109 and Asf1 also inhibit ARG1 under repressing conditions. This inhibition requires Asf1 binding to H3-H4 and Rtt109 KAT activity, but not tail acetylation of H3-H4 or K56 acetylation of H3. These observations suggest the existence of a unique mechanism of transcriptional regulation by Rtt109. Indeed, chromatin immunoprecipitation and genetic interaction studies support a model in which promoter-targeted Rtt109 represses ARG1 by silencing a pathway of transcriptional activation that depends on ASF1. Collectively, our results show that ARG1 transcription intensity at its induced and repressed set points is controlled by different mechanisms of functional interplay between Rtt109 and Asf1.