Covalent Structure of Calf‐Thymus ALK‐Histone

Highly purified calf thymus ALK‐histone (histone rich in alanine, lecine and lysine) was isolated from F2a2 histone fraction by ion‐exchange chromatography on Biorex 70 followed by gel filtration chromatography on Sephadex G‐100. Peptides obtained by enzymatic hydrolyses (trypsin, chymotrypsin, thermolysin) of native or maleylated protein were fractionated by ion‐exchange chromatography on Chromobeads P. Thermolysin peptides which account for 127 of the 129 residues of the protein provide overlaps of tryptic and chymotryptic peptides and led us to establish the complete amino‐acid sequence of ALK‐histone as follows: Ser1Gly‐Arg‐Gly‐Lys‐Gln‐Gly‐Gly‐Lys‐Ala‐10Arg‐Ala‐Lys‐Ala‐ Lys‐Thr‐Arg‐Ser‐Ser‐Arg20‐Ala‐Gly‐Leu‐Gln‐Phe‐Pro‐Val‐Gly‐Arg‐Val30‐His‐Arg‐Leu‐Leu‐Arg‐Lys‐Gly‐Asn‐Tyr‐Ala40‐Glu‐Arg‐Val‐Gly‐Ala‐Gly‐Ala‐Pro‐Val‐Tyr50‐Leu‐Ala‐Ala‐Val‐Leu‐Glu‐Tyr‐Leu‐Thr‐Al60‐Glu‐Ile‐Leu‐Glu‐Leu‐Ala‐Gly‐Asn‐Ala‐Ala70‐Arg‐Asp‐Asn‐Lys‐Lys‐Thr‐Arg‐Ile‐Ile‐Pro80‐Arg‐His‐Leu‐Gln‐Leu‐Ala‐Ile‐Arg‐Asn‐Asp90‐Glu‐Glu‐Leu‐Asn‐Lys‐Leu‐Leu‐Gly‐Lys‐Val100‐Thr‐Ile‐Ala‐Gln‐Gly‐Gly‐Val‐Leu‐Pro‐Asn110‐Ile‐Gln‐Ala‐Val‐Leu‐Leu‐Pro‐Lys‐Lys‐Thr120Glu‐Ser‐His‐His‐Lys‐Ala‐Lys‐Gly‐Lys129. The amino end is acetylated. The sequence of ALK‐histone is characterized by two hydro‐phobic regions, the first from Val‐43 to Ala‐70 and the second from Val‐100 to Pro‐117 and presents many repetitive or analogous sequences. The NH2‐terminal sequence of ALK‐histone is highly basic and shows a remarkable analogy with that of GRK‐histone. A cluster of five basic residues His‐His‐Lys‐Ala‐Lys‐Gly‐Lys is present at the COOH‐terminal end.