title: Identification and amino acid sequence of the deoxynucleoside triphosphate binding site in Escherichia coli DNA polymerase I.
abstract: We have labeled the large fragment of Escherichia coli DNA polymerase I (Pol I) with pyridoxal 5'-phosphate, a substrate binding site directed reagent for DNA polymerases [Modak, M. J. (1976) Biochemistry 15, 3620-3626]. A covalent attachment of pyridoxal phosphate to Pol I results in the loss of substrate binding as well as the polymerase activity. The inactivation was found to be strictly dependent on the presence of a divalent metal ion. Four moles of pyridoxal phosphate was found to react per mole of the enzyme, while in the presence of substrate deoxynucleoside triphosphate only 3 mol of pyridoxal phosphate was bound. To identify the substrate-protected site on the enzyme, tryptic peptides from enzyme labeled with pyridoxal phosphate and tritiated borohydride, in the presence and absence of substrate, were resolved on a C-18 reverse-phase column. A single peptide containing the substrate-protected site was identified and further purified. The amino acid composition and sequence analysis of this peptide revealed it to span residues 756-775 in the primary acid sequence of Pol I. Lys-758 of this sequence was found to be the site of the pyridoxal phosphate reaction. It is therefore concluded that Lys-758 is the site of binding for the metal chelate form of nucleotide substrates in E. coli DNA polymerase I.
authors.forename: A
authors.initials: A
authors.lastname: Basu
authors.forename: M J
authors.initials: MJ
authors.lastname: Modak
mesh_terms: D000595:Amino Acid Sequence; D001665:Binding Sites; D004256:DNA Polymerase I / Q000378:metabolism*; D003854:Deoxyribonucleotides / Q000378:metabolism*; D004926:Escherichia coli / Q000201:enzymology*; D010446:Peptide Fragments / Q000032:analysis; D011485:Protein Binding; D011732:Pyridoxal Phosphate
chemical_list: D003854:Deoxyribonucleotides; D010446:Peptide Fragments; D011732:Pyridoxal Phosphate; D004256:DNA Polymerase I