title: Excision repair characteristics of recB - res -  and uvrC -  strains of Escherichia coli.
abstract: An Escherichia coli strain carrying the recB21 and res-1 mutations showed an abnormally low level of colony-forming ability although it grew essentially normally in liquid medium. The recB21 res-1 strain showed little, if any, of the ultraviolet (UV)-induced deoxyribonucleic acid (DNA) breakdown characteristic of the res-1 mutant. Nevertheless, the double mutant was far more sensitive to UV than either the res-1 or the recB21 strain. When compared with a wild-type strain, the rate of release of dimers from UV-irradiated DNA was very slow in the recB21 res-1, but normal in the res-1 recB(+) or recB21 res(+) mutants. However, the ratio of dimer-to-thymine released into the acid-soluble fraction was three times higher than the wild type in recB21 res(+) and recB21 res-1 and only one-tenth as high as the wild type in res-1 rec(+). Alkaline sucrose gradient centrifugation revealed occurrence of single-strand incision of UV-irradiated DNA and the restitution of nicked DNA at a similar rate in the recB21 res-1 and recB21 res(+) strains. Mutants uvrC(-) showed increased amounts of nicks in their DNA with increasing incubation time after UV irradiation, although no detectable amounts of dimers were excised from UV-irradiated DNA. From these results, it is concluded that the increased sensitivity of the res-1 strain to UV light is due to a reduced ability to excise dimers from UV-irradiated DNA and that the high rate of UV-induced breakdown of DNA is not the primary cause. A possible role of uvrC gene in the excision repair is discussed.
mesh_terms: D000476:Alkanesulfonates / Q000494:pharmacology; D002499:Centrifugation, Density Gradient; D002999:Clone Cells; D003090:Coliphages / Q000187:drug effects / Q000528:radiation effects; D003470:Culture Media; D004260:DNA Repair; D004269:DNA, Bacterial / Q000032:analysis / Q000096:biosynthesis* / Q000528:radiation effects; D004926:Escherichia coli / Q000254:growth & development / Q000378:metabolism* / Q000528:radiation effects; D009154:Mutation; D009691:Nucleic Acid Denaturation; D011830:Radiation Effects; D011995:Recombination, Genetic; D013936:Thymidine / Q000378:metabolism; D014161:Transduction, Genetic; D014316:Tritium; D014466:Ultraviolet Rays
chemical_list: D000476:Alkanesulfonates; D003470:Culture Media; D004269:DNA, Bacterial; D014316:Tritium; D013936:Thymidine