title: Trimethoprim-induced DNA polymerase I deficiency in Escherichia coli K-12.
abstract: Curing of the mini-ColE1 plasmid pML21 was observed among cells of Escherichia coli K-12 strain C600(pML21) grown under subinhibitory conditions in the presence of trimethoprim, a specific inhibitor of dihydrofolate reductase. Some of the cured colonies showed (i) a reduction in frequency of transformation with pML21 compared with those of isogenic strains not treated with trimethoprim, (ii) loss of viability after acquisition of a recA mutation, and (iii) UV sensitivity greater than that of the original isogenic strain. These colonies therefore had PolA- phenotypes. Moreover, they were found to be deficient in DNA polymerase I activity in the in vitro assays, indicating the occurrence of a polA mutation in them. Many of the colonies with PolA- phenotypes were also thyA deoC mutants, and these mutations, in addition to the polA mutations, appeared to be involved in the expression of the PolA- phenotypes.
mesh_terms: D003086:Bacteriocin Plasmids; D002876:Chromosomes, Bacterial; D004256:DNA Polymerase I / Q000235:genetics / Q000378:metabolism*; D004259:DNA-Directed DNA Polymerase / Q000378:metabolism*; D004926:Escherichia coli / Q000201:enzymology* / Q000235:genetics; D005798:Genes, Bacterial; D008741:Methyl Methanesulfonate / Q000494:pharmacology; D009154:Mutation; D013941:Thymine / Q000378:metabolism; D014169:Transformation, Bacterial; D014295:Trimethoprim / Q000494:pharmacology*; D014466:Ultraviolet Rays
chemical_list: D014295:Trimethoprim; D008741:Methyl Methanesulfonate; D004256:DNA Polymerase I; D004259:DNA-Directed DNA Polymerase; D013941:Thymine