Postreplication DNA repair in ultraviolet-irradiated Micrococcus luteus.

Postreplication DNA repair was studies in three strains of Micrococcus luteus having different sensitivity to ultraviolet light: a wild type ATCC 5698, a ultraviolet-sensitive mutant G7, deficient in the incision step of repair and in ultraviolet-resistant transformant obtained from G7 by treatment with DNA of wild type cells, Trf(G7). It is shown that the G7 mutant has a low capacity for repair of postreplication DNA gaps compared with the wild type or Trf(G7). It seems to be that postreplication repari capacity contributes significantly to the ultraviolet resistance of M. luteus in addition to the excision repair. In contrast with G7 the size of the DNA fragments synthesized immediately after ultraviolet irradiation in the wild type (and Trf(G7)) seems to be much higher than that expected if each dimer produces one DNA gap in the daughter strand. Since this cannot only be explained by the excision of dimers from parental DNA we have suggested that a rapid repair of postreplication DNA gap occurs in M. luteus.