Chaperone-mediated acetylation of histones by Rtt109 identified by quantitative proteomics

► Quantitative proteomics determines the extent and specificity of histone acetylation. ► Rtt109-Vps75 preferentially acetylates histone H3 at K9 and K23. ► Rtt109-Asf1 displayed high substrate specificity towards H3K56. ► H4K12 can be acetylated by Rtt109-Vps75 but not by Rtt109-Asf1.