3′ → 5′ Exonucleases of DNA polymerases ε and δ correct base analog induced DNA replication errors on opposite DNA strands in Saccharomyces cerevisiae

The base analog 6-N-hydroxylaminopurine (HAP) induces bidirectional GC → AT and AT → GC transitions that are enhanced in DNA polymerase ε and δ 3′ → 5′ exonuclease-deficient yeast mutants, pol2-4 and pol3-01, respectively. We have constructed a set of isogenic strains to determine whether the DNA polymerases δ and ε contribute equally to proofreading of replication errors provoked by HAP during leading and lagging strand DNA synthesis. Site-specific GC → AT and AT → GC transitions in a Pol⁺, pol2-4 or pol3-01 genetic background were scored as reversions of ura3 missense alleles. At each site, reversion was increased in only one proofreading-deficient mutant, either pol2-4 or pol3-01, depending on the DNA strand in which HAP incorporation presumably occurred. Measurement of the HAP-induced reversion frequency of the ura3 alleles placed into chromosome III near to the defined active replication origin ARS306 in two orientations indicated that DNA polymerases ε and δ correct HAP-induced DNA replication errors on opposite DNA strands.