title: Eukaryotic DNA polymerase amino acid sequence required for 3'----5' exonuclease activity.
abstract: We have identified an amino-proximal sequence motif, Phe-Asp-Ile-Glu-Thr, in Saccharomyces cerevisiae DNA polymerase II that is almost identical to a sequence comprising part of the 3'----5' exonuclease active site of Escherichia coli DNA polymerase I. Similar motifs were identified by amino acid sequence alignment in related, aphidicolin-sensitive DNA polymerases possessing 3'----5' proofreading exonuclease activity. Substitution of Ala for the Asp and Glu residues in the motif reduced the exonuclease activity of partially purified DNA polymerase II at least 100-fold while preserving the polymerase activity. Yeast strains expressing the exonuclease-deficient DNA polymerase II had on average about a 22-fold increase in spontaneous mutation rate, consistent with a presumed proofreading role in vivo. In multiple amino acid sequence alignments of this and two other conserved motifs described previously, five residues of the 3'----5' exonuclease active site of E. coli DNA polymerase I appeared to be invariant in aphidicolin-sensitive DNA polymerases known to possess 3'----5' proofreading exonuclease activity. None of these residues, however, appeared to be identifiable in the catalytic subunits of human, yeast, or Drosophila alpha DNA polymerases.
authors.affiliation: Laboratory of Molecular Genetics, National Institute of Environmental Health Sciences, Research Triangle Park, NC 27709.
authors.forename: A
authors.initials: A
authors.lastname: Morrison
authors.forename: J B
authors.initials: JB
authors.lastname: Bell
authors.forename: T A
authors.initials: TA
authors.lastname: Kunkel
authors.forename: A
authors.initials: A
authors.lastname: Sugino
mesh_terms: D000595:Amino Acid Sequence; D001483:Base Sequence; D004252:DNA Mutational Analysis; D004257:DNA Polymerase II / Q000737:chemistry* / Q000378:metabolism; D005092:Exonucleases / Q000737:chemistry / Q000378:metabolism; D005800:Genes, Fungal; D008969:Molecular Sequence Data; D009841:Oligonucleotides / Q000737:chemistry; D016133:Polymerase Chain Reaction; D012441:Saccharomyces cerevisiae / Q000201:enzymology*; D016415:Sequence Alignment; D013329:Structure-Activity Relationship
chemical_list: D009841:Oligonucleotides; D004257:DNA Polymerase II; D005092:Exonucleases