3′ → 5′ Exonucleases of DNA Polymerases ϵ and δ Correct Base Analog Induced DNA Replication Errors on Opposite DNA Strands in Saccharomyces cerevisiae

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Abstract
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.

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