title: recA-dependent and recA-independent N-ethyl-N-nitrosourea mutagenesis at a plasmid-encoded herpes simplex virus thymidine kinase gene in Escherichia coli.
abstract: We have compared isogenic recA13/recA+ Escherichia coli K-12 strains for the induction by N-ethyl-N-nitrosourea (ENU) of forward mutations at a plasmid-encoded herpes simplex virus type 1 thymidine kinase (HSV-tk) gene. Treatment of plasmid-bearing bacteria with ENU resulted in a dose-dependent increase in the mutant frequencies of the chromosomal udk locus and of the plasmid HSV-tk locus in both recA13 and recA+ strains. Although the recA13 strain was considerably more sensitive to the cytotoxic effects of ENU treatment than was the recA+ strain, the ENU-induced mutation frequency at both loci was greater for the recA+ strain than for the recA13 strain. When plasmid DNA modified by in vitro reaction with ENU was used to transform recA13, recA+, and UV pre-irradiated recA+ strains, an increase in the HSV-tk mutant frequency was observed in all 3 cases. The induction of mutations in recA13 and recA+ strains followed a similar dose-response, while the ENU-induced HSV-tk mutant frequency was significantly greater for UV pre-irradiated recA+ bacteria. These results indicate that fixation of ENU-induced premutagenic lesions can occur by both recA-dependent and recA-independent pathways.
mesh_terms: D004260:DNA Repair / Q000187:drug effects; D004926:Escherichia coli / Q000187:drug effects / Q000235:genetics; D005038:Ethylnitrosourea / Q000633:toxicity*; D005467:Floxuridine / Q000494:pharmacology; D009154:Mutation / Q000187:drug effects*; D010957:Plasmids; D011938:Rec A Recombinases / Q000502:physiology*; D013014:SOS Response, Genetics / Q000187:drug effects; D018139:Simplexvirus / Q000201:enzymology / Q000235:genetics; D013937:Thymidine Kinase / Q000235:genetics*
chemical_list: D005467:Floxuridine; D013937:Thymidine Kinase; D011938:Rec A Recombinases; D005038:Ethylnitrosourea