Influence of temperature on platinum binding to DNA, cell killing, and mutation induction in Escherichia coli K-12 cells treated with cis-diamminedichloroplatinum(II).

Cell killing and specificity of mutation induction by treatment of Escherichia coli K-12 cells with cis-Pt(NH3)2Cl2 at various temperatures have been studied. Survival experiments show that the cell killing by cis-Pt(NH3)2Cl2 is enhanced with increasing temperature. This effect is explained by an increase in the amount of platinum bound to the DNA. The binding is the same in repair-proficient and in repair-deficient cells. However, the mutation induction in the lacI gene is much more strongly enhanced than could be expected from the increased platinum binding. This phenomenon is attributed to a different distribution of the induced lesions by cis-Pt(NH3)2Cl2 at various temperatures and not to an aberrant excision repair. Analysis of the induced lacI mutants revealed an increase in the percentage of nonsense mutants at higher temperature. Among the nonsense mutations, base-pair substitutions at GAG and particularly at GCG sequences are enhanced by the increasing temperature. The results are in agreement with our hypothesis that local denaturation of DNA, known to be promoted at higher temperature, is necessary for the formation of intrastrand cross-links at two guanine bases separated by a third base.