Postreplication repair and the fate of pyrimidine dimers in strains of Bacillus subtilis defective in excision repair or recombination

Several strains of Bacillus subtilis have been examined for postreplication repair after UV irradiation, Single in strand breaks were measured by sedimentation of DNA alkaline sucrose gradients, An enzymatic assay was used to monitor the fate of pyrimidine dimers, A preparation containing a damage-specific endonuclease introduced nicks at sites nearly all of the potential endonuclease-sensitive and allowed the measurement of a small number of pyrimidine dimers. The rate and extent of daughter strand joining was similar in two wildtype strains and strains deficient in excision repair (uvr-1, uvs-42) or DNA polymerase I (polAl). Two strains deficient in transduction (recF16, recG13) one strain deficient in both transduction and transformation (recE4) were unable to convert newly synthesized DNA to The data indicate that the uvr-1, high molecular weight. uvs-42, and polAl gene products are not involved in daughter strand gap filling and are consistent with the hypothesis an event that postreplication repair and transduction share that The results sug- is not required for transformation, gest that recombinational postreplication repair leads to an equilibration of dimers between parental and daughter DNA.