Human spleen histone H4. Isolation and amino acid sequence.

The amino acid sequence of human spleen histone H4 was investigated as part of a study on histone evolution, following previous investigations of human spleen histones H2B (J. Biochem. 85, 615-624), H2A (J. Biochem. 88, 27-34), and H3 (J. Biochem. 90, 1205-1211). The H4 fraction was obtained as described previously and further purified by Bio-Gel P-60 chromatography. The purified H4 was digested with trypsin and the peptides were fractionated by repeated column chromatographies with reasonable recoveries. Certain peptides were sequenced, and three modified residues (alpha-N-Ac-Ser-1, epsilon-N-Ac-Lys-16, and epsilon-N-Me-Lys-20) and one heterogeneous residue (Asn/Asp-25), which is probably a result of postsynthetic deamidation, were found. Thus, the human H4 was deduced to have a sequence of 102 amino acid residues completely identical with that of calf thymus H4, including the presence of three modified residues and the absence of any variant sequence. It is concluded that the animal H4 sequences and their postsynthetic modifications have been strongly conserved during the evolutionary process leading to man, as strongly as or more strongly than the H3 sequence, and much more strongly than the H2A and H2B sequences.