Development of new tester strains derived from E. coli WP2 uvrA for the determination of mutational specificity

Abstract

We have developed a set of multipurpose tester strains (WP3101 to WP3106) derived from E. coli WP2 uvrA for the detection and classification of mutagens. Six kinds of F′ plasmid ( lacI, lacZ, proAB +) in strains CC101–CC106, each of which carried a different lacZ allele, were transferred to a Δ(lac–pro) derivative of WP2 uvrA. Assays for transitions and transversions are based upon Lac + reversion of a specific mutation located within the lacZ gene on an F′ plasmid in strains WP3101–WP3106. In addition, the trpE65(ochre) allele in the same strains is available for Trp + reversion assays. Using the new tester strains, we investigated the mutational specificities of various chemical mutagens. Base analog mutagens and alkylating mutagens induced specific types of base substitutions. G:C→A:T transitions and G:C→T:A transversions predominated in mutagenesis induced by 4-nitroquinoline 1-oxide. Only a slight increase in G:C→T:A transversions was observed in cells treated with 2-(2-furyl)-3-(5-nitro-2-furyl)acrylamide (AF-2), although the potent mutagenicity of AF-2 was detected in a concurrent Trp + reversion assay in the same strain. Sodium azide, on the other hand, was negative in the Trp + reversion assay but specifically induced G:C→A:T transitions. Present finding suggested that target sites for AF-2- and azide-induced lesions may largely depend on sequence context.