Acetylates newly synthesized histones during DNA replication. Highly specific in vitro for the non-acetylated H4 which is acetylated sequentially at 'Lys-12' and 'Lys-5' into a di-acetylated form. acetyl-CoA + L-lysyl-[protein] = CoA + H(+) + N(6)-acetyl-L-lysyl-[protein] Inhibited by 5 mM of zinc, copper and iron. Unaffected by low concentrations of detergents and irreversibly inactivated by 2% ethanol, isopropanol or dimethyl sulfoxide. Optimum pH is 8.2-8.5. Optimum temperature is 37 degrees Celsius. Heteromer of HAT1/p50 and p45 subunits. Found in the dry embryo (at protein level). Maximum level of expression 22 hours after start of seed imbibition. Belongs to the HAT1 family.