Sequential polypeptides (Lys-Gly-Gly)5 and (Lys-Gly-Gly)10 were synthesized as models for the N-terminal region of H4 histone and their interactions with DNA were studied. The ability of (Lys-Gly-Gly)10 to precipitate DNA was found to be much higher than that of (Lys-Gly-Gly)5. For example, at the physiological salt concentration, (Lys-Gly-Gly)10 precipitates DNA but (Lys-Gly-Gly)5 does not. Both peptides could be acetylated by a partially purified histone acetyltransferase preparation derived from calf thymus. epsilon-Amino groups of lysyl residues were the sites of the acetylation. DNA-cellulose chromatography of the products indicated that acetylation weakened the interaction of the peptides with DNA.