title: Plasmid pKM101-dependent repair and mutagenesis in Escherichia coli cells with mutations lexB30 tif and zab-53 in the recA gene.
abstract: Bacterial survival after UV irradiation was increased in E. coli K12 lexB30 and tif zab-53 mutants harboring plasmid pKM101. Mutagenesis in response to UV was observed in these bacteria which, in absence of pKM101, are not UV-mutable. The mutator effect observed in unirradiated wild-type cells containing pKM101 was higher than incubation at 30 degrees C with adenine than at 37 degrees C. This effect was still enhanced by tif mutation, even in the tif zab-53 strain, but it was abolished by lexB30 mutation. In the tif zab-53 (pKM101) strain, repair and mutagenesis of UV-irradiated phage lambda was observed, but not in the lexB30 mutant carrying pKM101. The pKM101 mutant, pGW1, was unable to protect tif zab-53 bacteria against killing by UV, whereas the protection of lexB30 was intermediate; moreover, it did not promote the mutator effect at 30 degrees C or enhance phage repair and mutagenesis in tif zab-53 cells. All UV-induced bacterial mutations in lexB30 (pKM101) strain were suppressors; in contrast, true revertants were found after UV irradiation of the tif zab-53 (pKM101) cells. We suggest that the constitutive activity of RecA protein is enough for the production of UV-promoted suppressor mutations, whereas true reversions require a more active form of this protein which could exert its effects directly or by acting at a regulatory level on other cellular functions.
mesh_terms: D004260:DNA Repair; D004269:DNA, Bacterial / Q000528:radiation effects; D004926:Escherichia coli / Q000235:genetics* / Q000528:radiation effects; D009154:Mutation; D010641:Phenotype; D010957:Plasmids; D014466:Ultraviolet Rays
chemical_list: D004269:DNA, Bacterial