title: Plasmid pGW16, a derivative of pKM101, increases post-UV DNA synthesis, but sensitises some strains of Escherichia coli to UV.
abstract: Plasmid pKM101, which carries muc genes that are analogous in function to chromosomal umu genes, protected Escherichia coli strains AB1157 uvrB+ umuC+, JC3890 uvrB umuC+, TK702 uvrB+ umuC and TK501 uvrB umuC against ultraviolet irradiation (UV). Plasmid pGW16, a derivative of pKM101 selected for its increased spontaneous mutator effect, also gave some protection to the UmuC-deficient strains, TK702 and TK501. However, it sensitised the wild-type strain AB1157 to low, but protected against high doses of UV, whilst sensitising strain JC3890 to all UV doses tested. Even though its UV-protecting effects varied, pGW16 was shown to increase both spontaneous and UV-induced mutation in all strains. Another derivative of pKM101, plasmid pGW12, was shown to have lost all spontaneous and UV-induced mutator effects and did not affect post-UV survival. Plasmids pKM101 and pGW16 increased post-UV DNA synthesis in strains AB1157 and TK702, whereas pGW12 had no effect. Similarly, the wild-type UV-protecting plasmids R46, R446b and R124 increased post-UV DNA synthesis in strain TK501, but the non-UV-protecting plasmids R1, RP4 and R6K had no effect. These results accord with the model for error-prone DNA repair that requires umu or muc gene products for chain elongation after base insertion opposite non-coding lesions. They also suggest that the UV-sensitizing effects of pGW16 on umu+ strains can be explained in terms of overactive DNA repair resulting in lethal, rather than repaired UV-induced lesions.
authors.affiliation: Department of Pharmaceutics, School of Pharmacy, University of London, U.K.
authors.forename: C A
authors.initials: CA
authors.lastname: Little
authors.forename: D J
authors.initials: DJ
authors.lastname: Tweats
authors.forename: R J
authors.initials: RJ
authors.lastname: Pinney
mesh_terms: D002876:Chromosomes, Bacterial; D004249:DNA Damage; D004260:DNA Repair; D004269:DNA, Bacterial / Q000235:genetics / Q000528:radiation effects*; D004926:Escherichia coli / Q000235:genetics / Q000528:radiation effects*; D005798:Genes, Bacterial; D005838:Genotype; D009154:Mutation; D010957:Plasmids; D014466:Ultraviolet Rays
chemical_list: D004269:DNA, Bacterial