Reactions of the UVRABC excision nuclease with DNA damaged by diamminedichloroplatinum(II)

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Abstract
Mutants of Escherichia coil , which are blocked in excision repair ( uvr A6, uvr B5, or uvr C34) are exceptionally sensitive to the antitumor drug cis -Pt(II) (NH 3 ) 2 Cl 2 ( cis -DDP) but not to 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 uvr A, uvr B, and uvr C 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)(NH 3 ) 2 Cl 2 .