The amino acid sequence of boar H1t, a testis-specific H1 histone variant

H1t is a testis-specific H1 variant found in spermatocytes and spermatids of mammals. The complete amino acid sequence has been determined for H1t isolated from boar testes. The protein is composed of 211 amino acids with the composition 3 aspartic acids, 6 asparagines, 13 threonines, 21 serines, 7 glutamic acids, 7 glutamines, 15 prolines, 14 glycines, 37 alanines, 11 valines, 1 methionine, 3 isoleucines, 14 leucines, 1 tyrosine, 1 phenylalanine, 42 lysines, 15 arginines and a calculated molecular weight of 22,059 disregarding the post-translational acetylation of the amino-terminal alanine. The protein shows typical H1 domains with basic amino- and carboxyl-terminal regions separated by a conserved, presumably globular, core sequence. The core region is very homologous to the highly conserved core sequence found in somatic mammalian H1 histones but does differ from this sequence in 15 places. Accordingly, it may be appropriate to consider H1t as new variant category. The carboxyl-terminal half of H1t is distinguished from the standard somatic family by being somewhat shorter and by the presence of 10 arginine residues. In contrast to many H1 proteins, the carboxyl-terminal region of H1t does not show an obvious pattern of peptide repeats.