ROLE OF DEPURINATION IN MUTAGENESIS BY CHEMICAL CARCINOGENS

Abstract

The effect of modifying .vphi..chi.174 viral DNA by the chemical carcinogens .beta.-propiolactone, N-acetoxyacetylaminofluorene and anti-benzo[a]pyrene diol-epoxide was investigated by transfecting the modified DNA into Escherichia coli spheroplasts. Modification of the DNA in vitro by each of these agents was mutagenic for the .vphi..chi.174 amber mutants am3 and am86. Mutagenicity depended on the induction of the SOS response in the host spheroplasts. Heating .beta.-propiolactone-treated DNA at neutral pH caused strong inactivation such that the number of lethal hits was increased 4-fold. Sucrose gradient analysis showed the induction of alkali-labile sites in the heated DNA. The nicked circle assay with double-stranded .vphi..chi.174 DNA showed > 70% of these sites to be apurinic sites. Concomitantly with the production of these new sites, a strong increase in the mutation frequency was observed. This mutagenesis also depended upon the induction of the error-prone SOS response in the spheroplasts, as was previously shown to be the case for mutagenesis at putative apurinic sites induced directly by acid-heat treatment. Depurination may be of importance to the mechanism of mutagenesis by .beta.-propiolactone and other carcinogens.