MUTATIONAL SPECIFICITIES OF ENVIRONMENTAL CARCINOGENS IN THE LACL GENE OF ESCHERICHIA-COLI .7. THE HOST-MEDIATED ASSAY AND ITS COMPARISON WITH IN-VITRO MUTAGENESIS INDUCED BY 4-(METHYLNITROSAMINO)-1-(3-PYRIDYL)-1-BUTANONE

To investigate the influence of different types of metabolic activatio n (9,000 x g supernatant (S9) activation vs. a host-mediated approach) on 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK)-induced mutat ional specificity, we determined by DNA sequencing the distribution of forward mutations recovered in the N-terminal region of the lacI gene of Escherichia coli. After activation with the 59 liver fraction from rats treated with Aroclor 1254, a diverse spectrum of mutations was r ecovered, with 55% of the events being G:C-->A:T transitions. In contr ast, after the host-mediated assay in mice, G:C-->A:T transitions acco unted for over 94% of the mutations recovered. Generally, NNK metaboli sm can proceed through two distinct pathways, involving either alpha-m ethyl or methylene hydroxylation. These two pathways produce different distributions of DNA damage. The difference in the mutational spectra we observed thus likely reflects the difference in the contributions of each pathway under the two different treatment conditions. (C) 1993 Wiley-Liss, Inc.