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 i n DNA, making it impossible to determine which type of adduct causes w hich mutation and why, Adduct site-specific mutagenesis studies, in wh ich a single adduct is built into a vector, can be used to overcome th is 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 corres ponding mutagen/carcinogen. Mutations induced by a particular mutagen/ carcinogen can be influenced by DNA sequence context, mutagen/carcinog en dose (and other changes in conditions), level of SOS induction, cel l type and other factors, Thus, it is important to match the condition s of the adduct study versus the mutagen/carcinogen study as closely a s possible, DNA sequence context can profoundly affect the quantitativ e and qualitative pattern of adduct mutagenesis, which is addressed, I n vitro studies with DNA polymerases, frameshift mutagenesis and semi- targeted mutagenesis, whereby a mutation is induced near but not at th e site of the adduct, are each discussed, Finally, the relationship be tween structural studies on adducts and mutagenesis is considered.