Effects of benzo[ a]pyrene diol epoxide adducts on DNA synthesis in mammalian cells

Abstract

The replication of DNA containing anti-benzo[ a]pyrene diol epoxide (BPDE) adducts was studied in mammalian cells by first treating SV40 virus with BPDE in vitro, then infecting cells with virus containing a known number of adducts in the DNA. Viral transcription products necessary for replication were supplied by co-infection with an untreated virus containing a deletion as a DNA marker. Thus, only replicative effects of BPDE adducts were manifested. Delayed replication of the DNA from BPDE-treated virus, relative to the DNA containing the deletion, was observed, but in time most or all of the infecting molecules were able to replicate. The results are consistent with the hypothesis that adducts of BPDE in DNA block DNA synthesis in vivo, as they do in vitro, and that the block is gradually overcome by a repair mechanism that eliminates the adducts responsible for blockage or by delayed replicative bypass of the adducts. In spite of the ability of the system to overcome the delay in replication, the viability of the BPDE-treated virus in plaque assay was low, suggesting a persistent defect in transcription or a high level of error in repair or bypass replication.