Discrimination of mutagenic intermediates derived from alkylating agents by mutational patterns generated in Escherichia coli.
Reactive intermediates (ultimate mutagens/carcinogens) generated by alkylating agents are unstable and difficult to characterize by chemical means. We have used a genetic system to distinguish the in vivo interactions of eight carcinogenic methylating agents and five ethylating agents by the patterns of induced mutations at different target sites in Escherichia coli WU3610. For this multiple locus assay, target sites were an amber (TAG) and an ochre (TAA) triplet, DNA encoding five suppressor tRNA anticodons, and one unidentified locus. Most of the mutations could be classified as specific sequence changes at the target loci by suppressor analysis using T4 bacteriophage. Ratios of the slopes of dose-response curves for induced mutations were used to generate a profile of preferred sites for mutagenesis independent of mutagen potency. 'Mutational fingerprints' derived from different methylating and ethylating agents were compared, as evidence for the existence of common intermediates responsible for their biological effects. Six methylating agents thought to act via SN1 mechanisms were found to generate similar mutational patterns, indicative of a common mechanism, while two methylating agents reacting via SN2 mechanisms gave different patterns. The mutational fingerprints of SN1- and SN-type ethylating agents were also distinct. Mutational fingerprints may be useful in distinguishing the interactions of different ultimate mutagens.
Elespuru
R K
RK
Laboratory of Chemical and Physical Carcinogenesis, NCI-Frederick Cancer Research and Development Facility, MD 21702-1201.
Stupar
L L
LL
Gordon
J A
JA
D000477:Alkylating Agents / Q000378:metabolism*; D002874:Chromosome Mapping; D004269:DNA, Bacterial / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D004926:Escherichia coli / Q000235:genetics*; D009153:Mutagens / Q000378:metabolism*; D009154:Mutation; D010641:Phenotype
D000477:Alkylating Agents; D004269:DNA, Bacterial; D009153:Mutagens