Repair of plasmid DNA damaged in vitro with cis- or trans-diamminedichloroplatinum(II) in Escherichia coli.

Plasmid pBR322 was modified in vitro with the antitumor compound cis-diamminedichloroplatinum(II) (cis-DDP) or the isomeric trans-DDP. The numbers of platinum adducts were determined by atomic absorption spectrophotometry. DNA-repair-proficient and various DNA-repair-deficient (uvrB, uvrD, recB and recA) strains of Escherichia coli were transformed by the damaged plasmids and the ratios of the transformation frequencies of cells by damaged plasmids relative to those by untreated plasmids were determined. Results of transformation assays indicated that the uvrB gene function was essential for repair of plasmid DNA damaged with cis-DDP. A functional recA gene product seemed to be of minor importance for repair of plasmids damaged with cis-DDP. trans-DDP had a different effect on plasmid DNA. trans-DDP-modified DNA was better able to transform cells than cis-DDP-modified DNA, and the DNAs appeared to be repaired differently. Prior induction of SOS functions increased the survival of plasmids treated with cis-DDP in wild-type and uvrD mutants, but did not increase the survival of plasmids damaged with trans-DDP in these strains. In in vitro repair experiments, plasmid DNA modified with cis-DDP was more readily incised by the UVRABC excinuclease than that modified with trans-DDP.