Epistatic analysis of the roles of the RAD27 and POL4 gene products in DNA base excision repair in S. cerevisiae.

The cellular role of the DNA polymerase encoded by the Saccharomyces cerevisiae POL4 gene is unclear. We have used an epistasis analysis to investigate whether the proteins encoded by the POL4 and RAD27 genes participate in alternative, non-redundant subpathways of DNA base excision repair (BER). We constructed strains in which the genes were deleted singly or in combination and have examined their sensitivity to DNA damaging agents as well as spontaneous mutation frequency. The double deletion strain is no more sensitive to damaging agents and has no higher spontaneous mutation frequency than the most sensitive single mutant. These data indicate that the protein encoded by the POL4 gene does not participate in a non-redundant subpathway of base excision repair under these conditions. We discuss the implications of these results in light of the recent classification of the POL4 gene product as a member of the DNA polymerase lambda family.