Structural and biochemical investigations of the Rtt109‐histone chaperone complexes

Abstract

Reversible acetylation of lysine 56 of histone H3 (H3‐K56) is critical for DNA replication, repair and transcription in S. cerevisiae. Recent evidence suggests the acetylation of H3‐K56 is catalyzed by Rtt109‐histone chaperone complexes. Rtt109 bears no apparent sequence similarity to known histone acetyltransferases (HATs), thus it likely represents a novel HAT. The association of Rtt109 with either of the histone chaperones Asf1 or Vps75 is critical for increasing the efficiency of H3‐K56 acetylation in vitro and in vivo. While Asf1 has been directly linked to H3‐K56 acetylation in vivo, the functions of the Rtt109‐Vps75 complex are unclear. Using X‐ray crystallography and biochemical analyses, we are characterizing the structure and functions of the Rtt109‐Vps75 complex in vitro. We find that while Rtt109‐Vps75 prefers to acetylate H3‐K56, Rtt109‐Vps75 can also efficiently acetylate K9 and K27 of H3, while Rtt109‐Asf1 greatly prefers H3‐K56 over other sites within H3. Furthermore, the tail of H3 is required for efficient acetylation of H3‐K56 by Rtt109‐Vps75 but not for Rtt109‐Asf1, suggesting that substrate recognition and site specificity of Rtt109 may be modulated by the associated histone chaperone. This research is funded by grants from the National Institutes of Health and a pre‐doctoral fellowship from the American Heart Association.