Chaperone Control of the Activity and Specificity of the Histone H3 Acetyltransferase Rtt109

Banting and Best Department of Medical Research, Terrence Donnelly Centre for Cellular and Biomolecular Research (CCBR), University of Toronto, 160 College St, Toronto, Ontario M5S 3E1, Canada; Laboratory of Chromatin Biology, The Rockefeller University, 1230 York Ave, Box 78, New York, NY 10065, USA; Department of Cell Biology, Albert Einstein College of Medicine, 1300 Morris Park Avenue, Bronx, NY 10461, USA; Department of Biochemistry, University of Toronto, Toronto, Ontario M5S 3E1, Canada; Department of Molecular Genetics, University of Toronto, Toronto, Ontario M5S 3E1, Canada; Department of Cellular and Molecular Pharmacology, University of California San Francisco, San Francisco, CA 94143, USA

^* To whom correspondence should be addressed. Email: jack.greenblatt{at}utoronto.ca.

	Abstract

Acetylation of S.cerevisiae histone H3 on K56 by the histone acetyltransferase (HAT) Rtt109 is important for repairing replication-associated lesions. Rtt109 purifies from yeast in complex with the histone chaperone Vps75, which stabilizes the HAT in vivo. A whole genome screen to identify genes whose deletions have synthetic genetic interactions with rtt109 suggests Rtt109 has additional functions to DNA repair. We show that, in addition to its known H3K56 acetylation activity, Rtt109 is also a H3-K9 HAT, and that Rtt109 and Gcn5 are the only H3-K9 HATs in vivo. Rtt109's H3-K9 acetylation activity in vitro is enhanced strongly by Vps75. Another histone chaperone, Asf1, as well as Vps75 are both required for H3-K9ac in vivo by Rtt109, whereas H3-K56ac in vivo requires only Asf1. Asf1 also physically interacts with the nuclear Hat1/Hat2/Hif1 complex that acetylates H4-K5 and H4-K12. We suggest Asf1 is capable of assembling into chromatin H3-H4 dimers di-acetylated on both H4-K5,12 and H3-K9,56.