Mutants of Escherichia coli, which are blocked in excision repair (uvrA6, uvrB5, or uvrC34) are exceptionally sensitive to the antitumor drug cis-Pt(II)(NH3)2Cl2 (cis-DDP) but not the trans isomer. Plasmid DNA, damaged by either the cis or trans compound and treated with the UVRABC excision nuclease was cut as shown by conversion of supercoiled DNA to relaxed forms. All three protein products of the uvrA, uvrB, and uvrC genes were required for incision. End-labeled fragments damaged with cis-DDP and reacted with the UVRABC nuclease were cut at the 8th phosphodiester bond 5' and at the 4th phosphodiester bond 3' to adjacent GG's. DNA treated with trans-DDP was not cut appreciably at adjacent GG's by the repair enzyme as subsequent analysis of reaction products after enzyme digestion gave a pattern similar to those obtained with control untreated fragments. The results indicate that the UVRABC nuclease may promote cell survival by the removal of adjacent GG's which are crosslinked by cis-Pt(II)(NH3)2Cl2.

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The anti-tumor drug cis-platinum(II)diamminodichloride (PDD) induced extensive filamentation in wild-type Escherichia coli and in mutants lacking certain deoxyribonucleic acid (DNA) repair functions (uvrA, recB, recC, and polA); viability of repair-deficient mutants treated with PDD was significantly less than that of wild-type cells. PDD was highly toxic to lexl, lexl uvrA6 (where its effect was cummulative), and recA13 mutants, all of which were killed without formation of filaments. 'H-thymine incorporated into DNA of cells subsequently treated with PDD became trichloroacetic acid-soluble at rates similar to those observed after exposure to comparable doses of ultraviolet light (UV) or mitomycin C. PDD, like UV, induced extensive degradation of DNA in recA organisms. After a 30-min lag, PDD inhibited significantly the synthesis of DNA but not of ribonucleic acid or protein in E. coli. However, the relative differences between rates of DNA synthesis observed in PDD-treated and control cells decreased substantially when the duration of pulses (3H-thymine) was prolonged from 2 to 5 min. These observations suggest that PDD-induced damage to DNA is reversible, possibly by defined mechanisms of excision and recombination repair. 'Article no. 6329 from the Michigan Agricultural Experiment Station.

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