The role of adduct site-specific mutagenesis in understanding how carcinogen-DNA adducts cause mutations: perspective, prospects and problems.

Usually, a particular mutagen/carcinogen forms adducts at many sites in DNA, making it impossible to determine which type of adduct causes which mutation and why. Adduct site-specific mutagenesis studies, in which a single adduct is built into a vector, can be used to overcome this problem. The adduct can be situated in double-stranded DNA, single-stranded DNA or in a single-stranded gap, and the benefit and concerns associated with each are addressed. An adduct site-specific study is most useful when it is compared to a mutagenesis study with its corresponding mutagen/carcinogen. Mutations induced by a particular mutagen/carcinogen can be influenced by DNA sequence context, mutagen/carcinogen dose (and other changes in conditions), level of SOS induction, cell type and other factors. Thus, it is important to match the conditions of the adduct study versus the mutagen/carcinogen study as closely as possible. DNA sequence context can profoundly affect the quantitative and qualitative pattern of adduct mutagenesis, which is addressed. In vitro studies with DNA polymerases, frameshift mutagenesis and semi-targeted mutagenesis, whereby a mutation is induced near but not at the site of the adduct, are each discussed. Finally, the relationship between structural studies on adducts and mutagenesis is considered.