3'-]5'-EXONUCLEASES OF DNA-POLYMERASE-EPSILON AND DNA-POLYMERASE-DELTA 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 epsilon and delta 3' --> 5' exonuclease-deficient yeast mutants, pol2- 4 and pol3-01, respectively. We have constructed a set of isogenic str ains to determine whether the DNA polymerases delta and epsilon contri bute equally to proofreading of replication errors provoked by HAP dur ing leading and lagging strand DNA synthesis. Site-specific GC --> AT and AT --> GC transitions in a Pol(+), pol2-4 or pol3-01 genetic backg round were scored as reversions of ura3 missense alleles. At each site , reversion was increased in only one proofreading-deficient mutant, e ither pol2-4 or pol3-01, depending on the DNA strand in which HAP inco rporation presumably occurred. Measurement of the HAP-induced reversio n frequency of the ura3 alleles placed into chromosome III near to the defined active replication origin ARS306 in two orientations indicate d that DNA polymerases epsilon and delta correct HAP-induced DNA repli cation errors on opposite DNA strands.