title: Involvement of basic amino acids in the activity of a nucleic acid helix-destabilizing protein.
abstract: Under conditions of low ionic strength, ribonuclease A, which binds more tightly to single- than to double-stranded DNA, lowers the melting temperature of DNA helices (Jensen and von Hippel (1976) J. Biol. Chem. 251, 7198-7214). The effects of chemical modification of lysine and arginine residues on the helix-destabilizing properties of this protein have been examined. Removal of the positive charge on the lysine epsilon-amino group, either by maleylation or acetylation, destroys the ability of RNAase A to lower the Tm of poly[d(A-T)]. However, reductive alkylation of these residues, which has not effect on charge, yields derivatives which lower the Tm by only about one-half that seen with unmodified controls. Phenylglyoxalation of arginines can largely remove the Tm-depressing activity of RNAase A. RNAase S, which is produced by cleavage of RNAase A between amino acids 20 and 21, possesses DNA helix-destabilizing activity comparable to that of the parent protein, whereas S-protein (residues 21-124) increases poly[d(A-T)] Tm and S-peptide (1-20) has no effect on Tm. These results suggest that specific location of several basic amino acids situated on the surface of RNAase A is largely responsible for this protein's DNA melting activity.
mesh_terms: D000215:Acylation; D001120:Arginine; D002942:Circular Dichroism; D004265:DNA Helicases / Q000378:metabolism*; D004268:DNA-Binding Proteins; D004720:Endonucleases; D007700:Kinetics; D008239:Lysine; D008745:Methylation; D009690:Nucleic Acid Conformation; D009994:Osmolar Concentration; D010658:Phenylglyoxal / Q000494:pharmacology; D011067:Poly dA-dT; D011487:Protein Conformation; D012259:Ribonuclease, Pancreatic; D012260:Ribonucleases; D014764:Viral Proteins
chemical_list: D004268:DNA-Binding Proteins; D014764:Viral Proteins; C060035:gp32 protein, Enterobacteria phage T4; C027729:helix-destabilizing proteins; D011067:Poly dA-dT; D001120:Arginine; D004720:Endonucleases; D012260:Ribonucleases; D012259:Ribonuclease, Pancreatic; D004265:DNA Helicases; D008239:Lysine; D010658:Phenylglyoxal