The mutation spectrum induced by the widely used antitumor drug cis-diamminedichloroplatinum(II) (cis-DDP) showed that cisDDP{d(ApG)} adducts, although they account for only 25% of the lesions formed, are =5 times more mutagenic than the major GG adduct. We report the construction of vectors bearing a single cisDDP{d(ApG)} lesion and their use in mutagenesis experiments in Escherichia coli. The mutagenic processing of the lesion is found to depend strictly on induction of the SOS system of the bacterial host cells. In SOS-induced cells, mutation frequencies of 1-2% were detected. All these mutations are targeted to the 5' base of the adduct. Single A -+ T transversions are mainly observed (80%), whereas A -* G transitions account for 10% of the total mutations. Tandem base-pair substitutions involving the adenine residue and the thymine residue immediately 5' to the adduct occur at a comparable frequency (10%). No selective loss of the strand bearing the platinum adduct was seen, suggesting that, in vivo, cisDDP{d(ApG)} adducts are not blocking lesions. The high mutation specificity of cisDDP{d(ApG)}-induced mutagenesis is discussed in relation to structural data.During the past decade, progress in molecular biology allowed the development of strategies for elucidating the molecular mechanisms involved in processing the damages introduced in DNA by physical or chemical agents. A general procedure is to determine the forward mutation spectrum induced by a particular agent on a target DNA sequence (1). This approach allows definition of the general characteristics of the mutagenic processes, such as their genetic requirements and their specificity. However, these strategies are not sensitive enough to measure the relative contribution of different adducts in repair or mutagenesis events. This problem has been overcome by the use of synthetic oligodeoxyribonucleotides containing defined adducts located at precise sites (for review, see ref.2). When these adducts are introduced in a replicative vector and transfected into cells, several biological endpoints can be monitored: toxicity (3, 4), mutation efficiency and specificity (3-6), effect of the repair genotype of the host (7), and effect of surrounding sequences (3, 6). Furthermore, such modified oligonucleotides became useful tools for studying the structure of the DNA helix in the vicinity of the adduct (8-13) and precise biochemistry of repair (14-16).cis-Diamminedichloroplatinum(II) (cisDDP) is a widely used antitumor drug that binds to DNA, its main cellular target, by preferentially forming intrastrand crosslinks between the N7 atoms of adjacent purines (17)(18)(19). At low modification levels, the main adducts result from the chelation of two adjacent guanines [cisDDP{d(GpG)}], 65% of total lesions), whereas 25% of the adducts arise at 5' d(ApG) sequences. d(GpHpG) adduct (H = A, C, or T) and interstrand crosslinks altogether represent <10% of the total lesions (20-22).We have described the spectrum of mutations induced by cisDDP in Escherichia c...
