title: Evolution of dnaQ, the gene encoding the editing 3' to 5' exonuclease subunit of DNA polymerase III holoenzyme in Gram-negative bacteria.
abstract: The nucleotide sequences of the dnaQ genes from Salmonella typhimurium and Buchnera aphidicola, encoding the epsilon-subunit of the DNA polymerase III holoenzyme, have been determined. The Salmonella typhimurium dnaQ protein consists of 243 amino acid residues with a calculated molecular weight of 27224. The Buchnera aphidicola dnaQ protein contains 233 amino acid residues with a calculated molecular weight of 27170. A multiple sequence alignment of the amino acid sequences of the dnaQ proteins and those of DNA polymerase IIIs from Gram-positive bacteria produced six homologous segments. These homologous segments contain highly conserved amino acid sequence motifs involved in catalytically important metal ion bindings (ligands 1, 2 and 3). However, metal ligand 4 is found to be altered in the 3'-5' exonuclease domain of the family C DNA polymerases and dnaQ proteins in Gram-negative bacteria. From these results, we propose that the last common ancestor of the dnaQ gene of Gram-negative bacteria and the DNA polymerase III gene (pol C gene) of Gram-positive bacteria was a single gene containing both 3'-5' exonuclease and DNA polymerase domains and then the dnaQ gene separated from the polymerase gene in Gram-negative bacteria.
authors.affiliation: Department of Microbiology and Immunology, College of Medicine, The University of Arizona, Tucson 85724, USA.
authors.forename: Y
authors.initials: Y
authors.lastname: Huang
authors.forename: D K
authors.initials: DK
authors.lastname: Braithwaite
authors.forename: J
authors.initials: J
authors.lastname: Ito
mesh_terms: D000595:Amino Acid Sequence; D001483:Base Sequence; D004258:DNA Polymerase III / Q000235:genetics*; D004269:DNA, Bacterial; D019143:Evolution, Molecular; D006090:Gram-Negative Bacteria / Q000201:enzymology*; D008969:Molecular Sequence Data; D012486:Salmonella typhimurium / Q000201:enzymology*; D017386:Sequence Homology, Amino Acid
chemical_list: D004269:DNA, Bacterial; D004258:DNA Polymerase III