Effects of UV repair, error-prone repair and critical site of mutation on mutagenesis induced by N-nitrosamines.

Many N-nitrosamines have been assayed for mutagenic activity in bacteria but few have been systematically compared in a series of strains. In this study through the use of several Salmonella tester strains, we have examined the effects of Uvr repair, error-prone repair, and the critical site for mutation (GC or AT base pair) on the mutagenic activities of a diverse group of N-nitrosamines. We have employed the histidine autotrophs, TA1975 (uvrB+), TA1535 (uvrB-) and TA100 (uvrB-/pKM101) which are hisG46 strains, sensitive mainly to G-C base damage, and TA104 (uvrB-/pKM101), a hisG428 strain, which can be reverted at the hisG428 locus by damage to A-T base-pairs, or by suppression at G-C base pairs. The N-nitrosamines studied were, N-nitroso: dimethylamine, diethylamine, dipropylamine, dibutylamine, pyrrolidine, piperidine, morpholine, methylbenzylamine, bis-(2-hydroxypropyl)amine, bis-(2-oxopropyl)amine and 3,4-dichloropyrrolidine. For all of the nitrosamines larger than diethylnitrosamine (except for methylbenzylnitrosamine) mutagenesis was greatly enhanced (3-20 X) by the lack of uvrB activity, indicating that the DNA adducts produced by these nitrosamines can be classified as "bulky adducts". For most nitrosamines the plasmid, pKM101, enhanced mutagenesis in hisG46 strains, several fold, suggesting that error-prone DNA repair plays a role in mutagenesis by these compounds. All of the compounds tested were more mutagenic in TA100 than TA104 except diethylnitrosamine and methylbenzylnitrosamine which were more potent in TA104. Revertants induced by all of the nitrosamines in TA100 were due predominantly to damage at G-C base pairs. Revertants induced by all the nitrosamines except diethylnitrosamine and dibutylnitrosamine resulted mainly from damage to G-C base pairs in TA104.