Highly purified calf thymus ALK-histone (histone rich in alanine, leucine and lysine) was isolated from Fza2 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 ionexchange 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: Ser1-Gly-Arg-Gly-Lys-Gln-Gly-Gly-Lys-Ala-10Arg-Ala-Lys-Ala-LysThr-Arg-Ser-Ser-Arg20-Ala-Gly-Leu-Gln-Phe-Pro-Val-Gly-Arg-Val3o-His -Arg-Leu-Leu-Arg-LysGly-Asn-Tyr-Ala40-Glu-Arg-Val-Gly-Ala-Gly -Ma-Pro -Val-Tyr60-Leu -Ala-Ala-Val-Leu-Glu-TyrLeu-Thr-Ala~~-Glu-Ile-Leu-Gl~-Leu-Ala-Gly-Asn-Ala-Ala~~-Arg-Asp-Asn-Lys-Lys-Thr-Arg -IleIle-Proso-Arg-His-Leu-Gln-Leu-Ala-Ile-Arg-Asn-Aspso-Glu -Glu-Leu-Asn-Lys-Leu-Leu-Gly-LysVa1~~~-Thr-Ile-Ala-Gln-Gly-Gly-Val-Leu-Pro-Asn11o-Ile-Gln-Ala-Val-Leu-Leu-Pro-Lys-Lys-Thr~~~Glu-Ser-His-His-Lys-Ala-Lys-Gly-Lyslas.The amino end is acetylated. The sequence of ALK-histone is characterized by two hydrophobic 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 NH,-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 a t the COOH-terminal end.In the last five years refined methodology, combining selective and chromatographic or electrophoretic fractionation, has been set up for the separation of histones and has led to the isolation and Abbreviations. Dansyl, 5-dimethyl amino naphthalene-1-sulfonyl ; NMR, nuclear magnetic resonance.Nomenclature. The three-letter code used for the designation of histones emphasizes the three most abundant amino acids present in their molecule. GRK-histone = glycine, arginine, lysine-rich histone (formerly Fza1, histone IV or GAR-histone); KAS-histone = lysine, alanine, serine-rich histone (formerly Fzb, IIbz or LS-histone;) ARE-histone = alanine, arginine, glutamic acid-rich histone (formerly F, or histone 111) ; KAP-histone = lysine, alanine, proline-rich histone (formerly F, or very lysine-rich histone); ALKhistone = alanine, leucine, lysine-rich histone (formerly definition of five types of histones present in the nucleus of the somatic cell of mammals.The complete amino-acid sequence of three histones isolated from calf thymus has been determined: GRK-histone [1,2], 4] and AREhistone [5]. The primary structure of the KAPhistone from rabbit thymus is partially elucidated [61-A preliminary account of the complete aminoacid sequence of ALK-histone has already been reported [7]. Determination of the covalent structure of ALK-histone was initiated by an investigation of the tryptic and chymotryptic peptides from the native and maleylated protein...

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