EVIDENCES FOR POSSIBLE INVOLVEMENT OF RHP51 PROTEIN IN MITOTIC EVENTSINCLUDING CHROMOSOME SEGREGATION

To understand the role of the Rhp51 protein in Schizosaccharomyces pom be, we examined the phenotypes of the null mutant for the rhp51(+) gen e. Unlike Saccharomyces cerevisiae rad51 mutants, S. pombe rhp51 mutan ts (rhp51 Delta cells) displayed slow growth and heterogeneity in cell size, indicating perturbation of the cell cycle. Furthermore, many ab errant nuclear structures found in 4',6'-diamidino-2-phenylindole (DAP I)-stained rhp51 Delta cells and the caffeine hypersensitivity of the mutant cells suggested an involvement of the Rhp51 protein in normal c hromosome segregation. These data suggested that the Rhp51 proteins we re required for normal cell growth as well as a DNA repair pathway. Mo reover, rhp51 Delta mutants showed a considerable sensitivity to ultra violet (UV) light-irradiation as well as methyl methanesulfonate (MMS) treatment, indicating that the Rhp51 proteins are involved in both th e active excision mechanism of UV-induced DNA damage and recombination al repair in S. pombe. Taken together, we suggest that the role (s) of the Rhp51 protein in S. pombe may be different from those of Rad51 in S. cerevisiae.