Analysis of mutations induced in the SUP4-o gene of Saccharomyces cerevisiae by cis-diammine dichloroplatinum(II)

A collection of 196 mutations induced in the SUP4-o gene of yeast by treatment with cis-diammine dichloroplatinum(II) (cis-DDP) was characterized by DNA sequencing. All possible types of base pair substitution were identified as well as deletions, insertions and double mutations. Base pair changes at G.C sites predominated and were distributed throughout the gene. The majority of substitutions occurred at 5'-GG-3' and 5'-GA-3' sequences, potential sites of cis-DDP adducts. However, mutations were also detected at a number of other DNA sequences where cis-DDP has been found to bind in vitro or form adducts in vivo including 5'-AA-3', 5'-AG-3', 5'-GNG-3' and 5'-AAA-3'. The site specificity of cis-DDP mutagenesis argues that some of these sequences are significant targets for the induction of mutation in vivo despite the fact that they were considered to be weak binding sites for cis-DDP in vitro. In addition, the distribution of the substitutions within the SUP4-o gene indicates that DNA sequence context influences cis-DDP mutagenesis in vivo. Finally, our results suggest that intrastrand cross-links formed by cis-DDP might facilitate the gain or loss of single base pairs by stabilizing strand misalignments that template these events.