Histone chaperone-dependent acetylase that modifies 'Lys-9', 'Lys-14', 'Lys-23', 'Lys-27', and 'Lys-56' on histone H3 (H3K9Ac, H3K14Ac and H3K23Ac, H3K27Ac, and H3K56Ac) to promote nucleosome assembly, genomic stability, DNA repair and transcriptional regulation during mitotic S-phase (PubMed:31194870, PubMed:17046836, PubMed:17369253, PubMed:17320445, PubMed:17272723, PubMed:18723682, PubMed:20560668, PubMed:21256037, PubMed:29300933, PubMed:19172748, PubMed:19683497). Its residue selectivity is influenced by the acetylation status of histone H3, and also the presence of histone chaperone ASF1 that shifts selectivity to 'Lys-56' when H3K14Ac is already present (PubMed:31194870). H3K56 acetylation weakens the interaction between the histone core and the surrounding DNA in the nucleosomal particle and drives chromatin disassembly (PubMed:18577595). Autoacetylates (PubMed:18568037, PubMed:18707894, PubMed:18719104). Independently of acetyltransferase activity, stimulates histone deposition by VPS75 (PubMed:19172748). Involved in regulation of Ty1 transposition (PubMed:11779788). acetyl-CoA + L-lysyl-[histone] = CoA + H(+) + N(6)-acetyl-L-lysyl-[histone] acetyl-CoA + L-lysyl-[protein] = CoA + H(+) + N(6)-acetyl-L-lysyl-[protein] kcat is 0.11 sec(-1) with acetyl-CoA as substrate (at pH 7.5, 25 degrees Celsius in the presence of VPS75 chaperone) (PubMed:20560668). kcat is 0.19 sec(-1) with acetyl-CoA as substrate (at pH 7.0, 25 degrees Celsius in the presence of VPS75 chaperone) (PubMed:19172748). kcat is 0.0017 sec(-1) with acetyl-CoA as substrate (at pH 7.0, 25 degrees Celsius) (PubMed:19172748). kcat is 0.62 sec(-1) with histone H3 as substrate (at pH 7.5, 25 degrees Celsius in the presence of VPS75 chaperone (PubMed:20560668). kcat is 22.5 min(-1) with histone H3 (at pH 8, 30 degrees Celsius in the presence of VPS75 chaperone) (PubMed:18568037). kcat is 0.0033 sec(-1) with acetyl-CoA as substrate (at pH 7.0, 25 degrees Celsius) (PubMed:19172748). kcat is 0.11 sec(-1) with histone H3/H4 as substrate (at pH 7.0, 25 degrees Celsius in the presence of VPS75 chaperone) (PubMed:19172748). kcat is 0.0033 sec(-1) with histone H3/H4 as substrate (at pH 7.0, 25 degrees Celsius) (PubMed:19172748). Optimum pH is >8.5. Forms a complex composed of two RTT109 subunits and one VPS75 homodimer; each RTT109 subunit interacts predominantly with VPS75 instead of interacting with the other RTT109 subunit (PubMed:21256037, PubMed:20560668, PubMed:17320445, PubMed:31387991, PubMed:18719104). Interacts with VPS75; the interaction is direct (PubMed:31387991, PubMed:20560668, PubMed:17369253, PubMed:17690098, PubMed:17320445, PubMed:17272723, PubMed:18723682, PubMed:18719104, PubMed:21256037). Interacts (via C-terminus) with ASF1; the interaction is direct (PubMed:29300933, PubMed:31387991, PubMed:17690098, PubMed:17320445). Interacts with histone H3/H4 heterodimers via histone H3 (PubMed:21454705, PubMed:19172748). Expression peaks in cell cycle G1. Abolishes acetylation of histone H3 'Lys-56'; simultaneous disruption of GCN5 also abolishes acetylation of histone H3 'Lys-9' and 'Lys-27' (PubMed:21256037). Decreases acetylation of histone H3 'Lys-9' and 'Lys-23' (PubMed:19172748). Decreases HTA1 RNA level; simultaneous disruption of HIR1 or RTT106 alleviates the effect (PubMed:19683497). Increases sensitivity to methyl methane sulfonate, hydroxyurea, and camptothecin (genotoxic stress) (PubMed:18568037, PubMed:18719104). Present with 1140 molecules/cell in log phase SD medium. Belongs to the RTT109 family.