Repair of cyclobutane pyrimidine dimers and 6-4 photoproducts in the fission yeast Schizosaccharomyces pombe.

We have measured repair of both of the major lesions induced by ultraviolet irradiation (cyclobutane pyrimidine dimers and 6-4 photoproducts) in wild-type Schizosaccharomyces pombe and in selected rad mutants, including mutants with deletions in genes from the main phenotypic groups. We find that rad13 delta, rad15 and rad16 delta, which are the S. pombe homologues of the excision-defective Saccharomyces cerevisiae rad2, rad3 and rad1, respectively, repair lesions somewhat more slowly than the wild type, but still have considerable repair capacity. rad2 delta, also a presumed excision-defective mutant, behaves similarly. rad8 and rad9 delta, which belong to different phenotypic groups, repair lesions at the same rate as wild-type cells. These findings provide new evidence that S. pombe has a second repair system for removing ultraviolet damage, which is absent in S. cerevisiae. Surprisingly, this second mechanism repairs lesions very efficiently; its possible nature is discussed.