Specific binding of a nonhistone chromosomal protein from lymphocyte to DNA.

The isolation of a nonhistone chromosomal protein, NH30 000, from bovine lymphocytes by affinity chromatography on a DNA-agarose column is described. The procedure starts with nonhistone fraction NH4 obtained by hydroxyapatite chromatography as described previously [Blüthmann, H., Mrozek, S. & Gierer, A. (1975) Eur. J. Biochem. 58, 315-326]. Protein NH30 000 migrates as a single band with a molecular weight of 30 000 on sodium dodecylsulfate polyacrylamide gels. It contains, on a molar basis 25.3% acidic amino acids and 18.3% basic amino acid residues, 10.3% being lysine. End-group determination confirms that this protein is composed of one polypeptide chain with the NH2-terminal amino acid arginine. The binding of protein NH30 000 to native DNA of different molecular weights has been investigated by the nitrocellulose filter assay. The results suggest that in the presence of 0.2 M NaCl it binds about 30% of the DNA with binding sites every 1700 nucleotide pairs. Competition experiments show that protein NH30 000 exhibits a higher binding affinity for lymphocyte DNA in comparison to Escherichia coli DNA.