LACK OF CORRELATION BETWEEN IN-VITRO AND IN-VIVO REPLICATION OF PRECISELY DEFINED BENZ[A]ANTHRACENE ADDUCTED DNAS

Like other polycyclic aromatic hydrocarbons, certain metabolites of be nz[a]anthracene have been implicated as potent carcinogens. These effe cts are thought to be caused by the covalent binding of these species to nucleophilic groups on the bases of DNA. To address the molecular m echanisms by which these molecules induce mutations, this study employ ed oligonucleotides containing four site-specific N-6 adenine-benz[a]a nthracene diol epoxide adducts. Using a prokaryotic in vivo replicatio n system, we have shown that both non-bay region anti-trans-benz[a]ant hracene adducts are essentially nonmutagenic. In contrast, the bay reg ion anti-trans-benz[a]anthracene lesions do induce point mutations at the adduct site. The mutagenic frequency of these bay region lesions i s dependent on the stereochemistry about the adduct-forming bond, as w ell as the strain of Escherichia coli in which they are replicated. Th e ability of the bacterial replication machinery to bypass the lesions does not correlate with the differences observed in their mutagenesis . While both non-bay region adducts are readily bypassed in vivo, the bay region adducts are both blocking to approximately the same degree. In vitro studies of the interactions of E. coli DNA polymerase III wi th these adducts have also been undertaken to further dissect the rela tionship between adduct structure and biological activity.