Requirement of yeast DNA polymerase delta in post-replicational repair of UV-damaged DNA.

DNA lesions in the template strand pose a block to the replication machinery. Replication across such lesions may occur by a mutagenic bypass process in which a wrong base is inserted opposite the lesion or may involve processes that are relatively error-free. Genetic studies in the yeast Saccharomyces cerevisiae have indicated the requirement of REV3-encoded DNA polymerase in mutagenic bypass. The DNA polymerase responsible for error-free bypass, however, has not been identified, but genetic studies implicating proliferating cell nuclear antigen in this process have suggested that either DNA polymerase delta or DNA polymerase epsilon may be involved. Here, we use temperature-sensitive (ts) conditional lethal mutations of the S. cerevisiae POL2 and POL3 genes, which encode DNA polymerase epsilon and delta, respectively, and show that post-replicational bypass of UV-damaged DNA is severely inhibited in the pol3-3 mutant at the restrictive temperature. By contrast, the pol-2-18 mutation has no adverse effect on this process at the restrictive temperature. From these observations, we infer a requirement of DNA polymerase delta in post-replicative bypass of UV-damaged DNA.