title: Studies on the structure of mouse helix-destabilizing protein-1. DNA binding and controlled proteolysis with trypsin.
abstract: A mouse helix-destabilizing protein (HD protein-1) has been purified and characterized, and controlled tryptic digestion has been used to generate two large fragments of this protein and to study structural changes accompanying DNA binding. HD protein-1, a DNA-binding protein that has higher affinity for single-stranded DNA (ssDNA)-cellulose than for double-stranded DNA (dsDNA)-cellulose and is resistant to a dextran sulfate elution from ssDNA-cellulose, was purified from mouse myeloma by the method described by Herrick and Alberts (Herrick, G., and Alberts, B. M. (1976) J. Biol. Chem. 251, 2124-2132). HD protein-1 was heterogeneous with regard to apparent molecular weight (range of Mr = 24,000 to 33,000), but individual Mr species shared extensive primary structure homology as revealed by tryptic peptide mapping. The predominant species of this protein, Mr = 27,000, was resolved from other species and obtained in nearly homogeneous form by preparative isoelectric focusing. Mouse HD protein-1 was capable of lowering the Tm of poly[d(A-T)] by 25 degrees C, indicating that it is a helix-destabilizing protein. Sedimentation boundary analysis revealed that binding to ssDNA was noncooperative and that the binding site covered about 6 nucleotide residues. There was a 35% increase in the intrinsic tryptophan fluorescence of the protein in the presence of ssDNA, suggesting that structural change accompanies binding. Subcellular localization studies indicated that 75% of mouse HD protein-1 is nuclear, but not chromatin-associated, and primary structure analysis indicated that HD protein-1 is distinct from high mobility group proteins 1 and 2, histones, and P8 protein. Tryptic hydrolysis of HD protein-1 produced discrete, large fragments whose apparent molecular weights ranged from 19,000 to 24,000, and whose relative abundance was changed by the presence of ssDNA during the digestion. Thus, a Mr = 22,000 fragment (22 HDP*) predominated in the absence of ssDNA, and a Mr = 19,000, fragment (19 HDP*) predominated in the presence of ssDNA. Poly(dT) and denatured calf thymus DNA were more effective than were other polynucleotides tested in promoting accumulation of 19 HDP*; (dT)8 was as effective as were longer molecules of (dT)n, but (dT)4 and (dT)6 were much less effective, indicating that the binding site involved in 19 HDP* accumulation covered between 6 and 8 residues of (dT)n. Both 19 HDP* and 22 HDP* have the same COOH-terminal end and the same affinity for ssDNA-cellulose as does the native HD protein-1, indicating that a Mr = 8,000 sequence at the NH2-terminal end of HD protein-1 is not required for binding to ssDNA. Even though 22 HDP* retained the ability to bind to ssDNA, it could not be converted to 19 HDP* by further trypsin digestion.
mesh_terms: D000596:Amino Acids / Q000032:analysis; D000818:Animals; D002460:Cell Line; D004247:DNA / Q000378:metabolism*; D004265:DNA Helicases / Q000302:isolation & purification / Q000378:metabolism*; D004268:DNA-Binding Proteins; D000076245:Heterogeneous Nuclear Ribonucleoprotein A1; D034481:Heterogeneous-Nuclear Ribonucleoprotein Group A-B; D007700:Kinetics; D051379:Mice; D008970:Molecular Weight; D010446:Peptide Fragments / Q000032:analysis; D010954:Plasmacytoma; D011089:Polydeoxyribonucleotides / Q000494:pharmacology; D011485:Protein Binding; D011487:Protein Conformation; D012261:Ribonucleoproteins; D013347:Subcellular Fractions / Q000201:enzymology; D013951:Thymus Hormones; D014357:Trypsin; D014764:Viral Proteins
chemical_list: D000596:Amino Acids; D004268:DNA-Binding Proteins; D000076245:Heterogeneous Nuclear Ribonucleoprotein A1; D034481:Heterogeneous-Nuclear Ribonucleoprotein Group A-B; C000619657:Hnrnpa1 protein, mouse; D010446:Peptide Fragments; D011089:Polydeoxyribonucleotides; D012261:Ribonucleoproteins; D013951:Thymus Hormones; D014764:Viral Proteins; C060035:gp32 protein, Enterobacteria phage T4; C027729:helix-destabilizing proteins; D004247:DNA; D014357:Trypsin; D004265:DNA Helicases