HAT1 is a type B histone acetyltransferase that participates in the rapid acetylation of newly synthesized cytoplasmic histones, which are in turn imported into the nucleus for de novo deposition onto nascent DNA chains. Histone acetylation, mainly of soluble histone H4 at ’’Lys-5’’ and ’’Lys-12’’ and acetylates histone H2A at ’’Lys-5’’. HAT1 takes part in replication-dependent chromatin assembly. HAT1 acetylates soluble but not nucleosomal histone H4 at lysines 5 and 12, and to a lesser degree, histone H2A at lysine 5. HAT1 has intrinsic substrate specificity that modifies lysine in recognition sequence GXGKXG.