These data suggest that regioselectivity of histone acylation catalysts is determined by the combination of proximity to the catalytically active site and intrinsic reactivity of target Lys residues. Within CER, the Lys residue with higher intrinsic reactivity (in this case, H2BK108) is preferentially acylated. The acylation yield sharply decreases when the Lys residue is outside CER (e.g., H2BK108 using catalyst 1 or 3).