Inefficient proofreading and biased error rates during inaccurate DNA synthesis by a mutant derivative of Saccharomyces cerevisiae DNA polymerase delta.
DNA polymerase delta (pol delta) is a high fidelity eukaryotic enzyme that participates in DNA repair and is essential for DNA replication. Toward the goal of dissecting its multiple biological functions, here we describe the biochemical properties of Saccharomyces cerevisiae pol delta with a methionine replacing conserved leucine 612 at the polymerase active site. Compared with wild type pol delta, L612M pol delta has normal processivity and slightly higher polymerase specific activity. L612M pol delta also has normal 3' exonuclease activity, yet it is impaired in partitioning mismatches to the exonuclease active site, thereby reducing DNA synthesis fidelity. Error rates in vitro for L612M pol delta are elevated for both base substitutions and single base deletions but in a highly biased manner. For each of the six possible pairs of reciprocal mismatches that could arise during replication of complementary DNA strands to account for any particular base substitution in vivo (e.g. T-dGMP or A-dCMP for T to C transitions), L612M pol delta error rates are substantially higher for one mismatch than the other. These results provide a biochemical explanation for our observation, which confirms earlier genetic studies, that a haploid pol3-L612M S. cerevisiae strain has an elevated spontaneous mutation rate that is likely due to reduced replication fidelity in vivo.
Nick McElhinny
Stephanie A
SA
Laboratory of Molecular Genetics, NIEHS, National Institutes of Health, Department of Health and Human Services, Research Triangle Park, North Carolina 27709, USA.
Stith
Carrie M
CM
Burgers
Peter M J
PM
Kunkel
Thomas A
TA
D000595:Amino Acid Sequence; D002384:Catalysis; D004258:DNA Polymerase III / Q000235:genetics*; D004261:DNA Replication; D004271:DNA, Fungal / Q000235:genetics; D008969:Molecular Sequence Data; D009154:Mutation; D009690:Nucleic Acid Conformation; D011487:Protein Conformation; D012441:Saccharomyces cerevisiae / Q000235:genetics*
D004271:DNA, Fungal; D004258:DNA Polymerase III