Isolation by a New Method and Sequence Analysis of Chromosomal HMG-17 Protein from Porcine Thymus

Nonhistone chromosomal protein HMG-17 from porcine thymus has been isolated by extraction in boiling water, gel filtration and HPLC, and its complete primary structure (89 residues) has been determined. Peptides derived from enzymatic hydrolysis with trypsin, Staphylococcus aureus V-8 protease, Arg-C, and Glu-C proteinases were purified by HPLC and sequenced by the 4-(N,N-dimethylamino)azobenzene-4′- isothiocyanate/phenylisothiocyanate double coupling method. Porcine HMG-17 has a molecular mass of 9248 Da and a pI > 9.8. No glycosylation or methylation has been detected. The primary structure of this protein is almost identical to the sequence deduced from a cDNA clone derived from a human cell line. Porcine thymus HMG-17 differs from the human protein by only a single conservative substitution at position 64 (aspartic acid instead of glutamic acid). As in other HMG-17 proteins, the sequence is characterized by a lysine- and proline-rich central region, which has been implicated in DNA binding.