title: Post-UV survival and mutagenesis in DNA repair-proficient and -deficient strains of Escherichia coli K-12 grown in 5-azacytidine to inhibit DNA cytosine methylation: evidence for mutagenic excision repair.
abstract: Inhibition of cytosine methylation by growth in 5-azacytidine (5-azaC), did not affect the sensitivities to DNA damage induced by exposure to ultraviolet light (UV) of Escherichia coli K-12 strains AB1157 dcm+, which is fully DNA repair-proficient, LR68 (a dcm derivative of AB1157), JC3890 dcm+ uvrB, deficient in error-free excision repair, TK702 dcm+ umuC, deficient in error-prone repair, or TK501 dcm+ uvrB umuC, which lacks both excision repair and error-prone repair. However, growth in 5-azaC increased the post-UV survival of strains AB2463 recA(Def), AB2470 recB and AB2494 lexA(Ind-), which are deficient in the induction or expression of recombination repair or error-prone repair of DNA. Spontaneous mutation frequencies were increased in strains LR68, AB2463, AB2470 and AB2494 by growth in 5-azaC, but remained unaltered in strains AB1157, JC3890, TK702 or TK501. Growth in 5-azaC significantly increased UV-induced mutation frequencies in strains AB2463 and AB2470, significantly reduced UV-induced mutation in strain JC3890, but had little effect on UV-induced mutation in the other strains. The results suggest that 5-azaC may induce a normally error-free DNA repair pathway to become error-prone and therefore genotoxic.
authors.affiliation: Department of Pharmaceutics, School of Pharmacy, University of London, UK.
authors.forename: L
authors.initials: L
authors.lastname: Radnedge
authors.forename: R J
authors.initials: RJ
authors.lastname: Pinney
mesh_terms: D001374:Azacitidine / Q000494:pharmacology*; D003596:Cytosine / Q000378:metabolism*; D004260:DNA Repair / Q000187:drug effects / Q000235:genetics* / Q000528:radiation effects; D004269:DNA, Bacterial / Q000378:metabolism*; D004926:Escherichia coli / Q000187:drug effects / Q000235:genetics* / Q000528:radiation effects; D008745:Methylation; D016296:Mutagenesis / Q000187:drug effects* / Q000528:radiation effects; D014466:Ultraviolet Rays
chemical_list: D004269:DNA, Bacterial; D003596:Cytosine; D001374:Azacitidine