Induction of tandem-base change mutations.

Four databases with sequence changes for 12000 mutations in mammalian and bacterial cells were searched for genotoxic agents inducing tandem mutations, in which two adjacent base pairs are changed. Ultraviolet light induces about one CC > TT per 10-20 mutations, and other tandem-base changes at about half that frequency. There is strong evidence that cis-diammine dichloroplatinum (II) induces tandems. These results suggest that tandem-base changes are induced by agents that damage two adjacent base pairs in DNA. Tandems, particularly CC > TT, can be used as indicators of exposure to ultraviolet light, as in genes in skin cells exposed to sunlight. Oxidizing agents such as superoxide and ionizing radiation do not induce a significant level of tandem-base changes (such as CC > TT) in double-strand DNA, so such mutations are not a useful indicator of exposure to mutagens of this type. All conclusions are equally valid for bacterial and mammalian cells.