Histone chaperone-dependent acetylase that modifies 'Lys-56' of histone H3 (H3K56ac), which occurs predominantly in newly synthesized H3 molecule during G1, S-phase and G2/M of cell cycle (PubMed:17369611, PubMed:17690098, PubMed:20656950). Histone H3 'Lys-56' acetylation is required for S-phase-linked DNA damage tolerance and proper silencing in pericentromeric heterochromatin (PubMed:17369611). 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] Belongs to the RTT109 family.