Mutation and DNA modification in Salmonella exposed to N-nitrosodimethylamine under UVA- and sunlight-irradiation

Previously, we reported that when Salmonella typhimurium and Escherichia co li were treated with N-nitrosodimethylamine (NDMA) under irradiation with u ltraviolet-A (UVA), mutagenesis of the bacteria took place without external ly added activation enzymes. We also observed the formation of O-6-methylgu anine (O-6-meG), N-7-methylguanine (N-7-meG) and 7,8-dihydro-8-oxodeoxyguan osine (8-oxodG) in calf thymus DNA treated with NDMA plus UVA, In this stud y, we observed the mutagenicity of NDMA under irradiation of natural sunlig ht in S, typhimurium. Furthermore, we detected the formation of O-6-meG, N7 -meG and 8-oxodG in calf thymus DNA treated with NDMA plus simulated sunlig ht. Regarding the mutagenesis of S. typhimurium by NDMA plus UVA, we have n ow identified and quantified O-6-meG formed in the genomic DNA of the bacte ria under conditions of the mutagenesis. (C) 1999 Elsevier Science B.V. All rights reserved.