Delayed transfection of DNA after riboflavin mediated photosensitization increases G : C to C : G transversions of supF gene in Escherichia coli mutYstrain

We have previously reported that the majority of base substitution mutation s of the Escherichia coli supF gene induced by riboflavin mediated photosen sitization were G:C to C:G changes, in addition to G:C to T:A changes which were probably caused by 8-hydroxyguanine (oh(8)Gua), in wild type and mutM mutator mutant strains. This implies that lesions other than oh(8)Gua are produced by riboflavin-photosensitization. G:C to C:G base substitutions ha ve been found in the mutations induced by ionizing radiation and reactive o xygen species, as well as spontaneous mutation. To characterize the G:C to C:G mutation, riboflavin- photosensitized plasmid DNA carrying the supF gen e was left at room temperature for 5 h in the dark before transfection. The delayed transfection gave a mutational spectrum different from that for im mediate transfection. G:C to C:G transversions significantly increased in m utY mutator strain, in which the transversion was not detected in the immed iate transfection. Lesions causing G:C to C:G changes increased during 5-h holding after photosensitization and MutY protein presumably takes part in this type of base change mutation. (C) 1999 Elsevier Science B.V. All right s reserved.