Histone chaperone-dependent acetylase that modifies 'Lys-56' of histone H3 (H3K56ac), to promote genomic stability, DNA repair and transcriptional regulation during mitotic S-phase (PubMed:20601951, PubMed:20080646). Plays an important role in the regulation of white-opaque genotoxin induced-switching (PubMed:21749487). acetyl-CoA + L-lysyl-[histone] = CoA + H(+) + N(6)-acetyl-L-lysyl-[histone] Leads to a decreased pathogenicity in mice and increased susceptibility to killing by macrophages in vitro. Belongs to the RTT109 family.