Analysis of DNA repair pathways of Schizosaccharomyces pombe by means of swi-rad double mutants.

In Schizosaccharomyces pombe 11 different switching genes (swi1 to swi10 and rad22) are known which are involved in mating-type (MT) switching. Mutations in swi5, swi9, swi10 and rad22 also cause an increased radiation sensitivity. We tested whether the survival of these mutants after UV irradiation is influenced by caffeine. We included rad1 and rad13 mutants in our experiments which do not affect MT switching. Several double and triple mutants were constructed. We were able to assign the switching genes to different repair pathways: swi9 and swi10 are involved in excision repair, rad22 has a function in recombination repair, while swi5 appears to be involved in a hitherto unknown pathway. This 'swi5 pathway' is stimulated (!) by caffeine. Previously it was found that the swi5 mutation also reduces meiotic recombination. As to rad genes, we found a few inconsistencies with previous reports in the literature.