THE MAJOR MITOMYCIN C-DNA MONOADDUCT IS CYTOTOXIC BUT NOT MUTAGENIC IN ESCHERICHIA-COLI

To determine the mutagenic and genotoxic properties of the major guani ne N-2-adduct formed by the antitumor drug mitomycin C, we have synthe sized a decanucleotide, d(TTACG(MC)TATCT), containing the adduct, whic h was inserted into a gapped bacteriophage M13 genome. Analysis of the constructed genome indicated that 41% ligation of the adducted 10-mer occurred on both sides of the gap, whereas the control 10-mer ligated with 34% efficiency. After transfection of the adducted single-strand ed M13 DNA into Escherichia coli, the adduct was found to be highly ge notoxic. Viability of the adducted genome in a repair-competent strain was only 7%, which increased to 12% and 15% upon induction of SOS by irradiating the cells with 254-nm light at 20 and 50 J/m(2), respectiv ely. Even lower viability of 2%, 4.6%, and 0.2% was observed in uvrA, uvrB and uvrC strains, respectively, which increased up to 10-fold wit h SOS. An examination of the surviving phage populations revealed that the adduct was not detectably mutagenic. No mutants from the repair-p roficient strain were detected after analysis of more than 2500 progen y phage. Only 0.2% of the survivors were mutants in the uvrA strain. I t is uncertain, however, if they were induced by the adduct, since all the mutants showed untargeted mutations. We conclude that the major g uanine N-2-adduct formed by mitomycin C is cytotoxic but not appreciab ly mutagenic in E. coli.