title: Effect of the pKM101 plasmid on the repair of single-strand breaks in DNA induced by ionizing irradiation in Escherichia coli.
abstract: The effect of pKM101 plasmid on repair of single-strand breaks in DNA induced by 60Co-gamma irradiation in E. coli K12 AB1157 (wild type) and in its recA- and recB- mutant cells was studied by alkaline sucrose gradient sedimentation method. For quantitative analysis of sedimentation profiles we calculated the S1/2 values described by Veatch and Okada. The S1/2 values of unirradiated cells were 21.10, and after 200 Gray irradiation 11.35, due to the original incidence of single-strand breaks. The presence of pKM101 did not influence these values in either cases. This means that pKM101 had no effect on the rise of single-strand breaks in DNA. During a post-irradiation incubation period at 37 degrees C for 60 min the S1/2 value of the wild type strain increased from 11.35 to 19.22, that of the recB- from 11.50 to 15.23, while the S1/2 value of the recA- mutant did not change owing to the lack of repair of single-strand breaks. pKM101 plasmid markedly increased the S1/2 value in wild type strain and in recB- mutant, while it had no effect on S1/2 in recA- cells, during this post-irradiation incubation period. Thus the effect of pKM101 on the repair of single-strand breaks in DNA proved to be dependent on recA+ genotype. Nalidixic acid at 100 micrograms/ml concentration inhibited the repair of single-strand breaks in both wild type and recB- mutant cells harbouring pKM101 plasmid.
mesh_terms: D002499:Centrifugation, Density Gradient; D003037:Cobalt Radioisotopes; D004260:DNA Repair / Q000187:drug effects; D004269:DNA, Bacterial / Q000528:radiation effects*; D004926:Escherichia coli / Q000235:genetics*; D009154:Mutation; D009268:Nalidixic Acid / Q000494:pharmacology; D010957:Plasmids
chemical_list: D003037:Cobalt Radioisotopes; D004269:DNA, Bacterial; D009268:Nalidixic Acid