Sites of inhibition of in vitro DNA synthesis in carcinogen- and UV-treated Φ174 DNA

Abstract

THE availability of DNA molecules of known sequence and rapid methods for the determination of the sequence of particular DNA fragments^1–3 make it possible to investigate the molecular action of mutagens and carcinogens more closely^4,5. For example, there is considerable evidence that some types of lesion in DNA such as UV light-induced pyrimidine dimers and various chemical adducts are blocks to DNA synthesis both in vivo^6–9 and in vitro^10,11. The available data support the hypothesis that the block occurs at the level of the lesion on the template strand^10,11. We have used DNA containing such lesions on a template of known sequence for in vitro DNA synthesis by DNA polymerase 1 to investigate the site of the block at the level of the nucleotide sequence. This method allows us to determine both the site at which lesions capable of blocking synthesis by DNA polymerase occur and exactly where synthesis stops in relation to the lesion.