EXCISION-REPAIR REDUCES DOXORUBICIN-INDUCED GENOTOXICITY

LacI mutations induced by doxorubicin in a wild-type, uvr(A)BC repair-proficient E. coli strain were analyzed by DNA sequencing. These mutations were contrasted with mutations previously recovered from doxorubicin-treated uvrB- organisms in order to assess the role of excision repair in doxorubicin-induced genotoxicity. After a 30-min exposure of wild-type E. coli to 330 muM doxorubicin, survival was 34% and the overall lacI mutation frequency increased 1.8-fold to 340 X 10(-8). The distribution of doxorubicin-induced mutants among subclasses of mutation involving the i(-d) and lac operator regions differed significantly between repair-proficient and -deficient strains. Distributional differences appeared to result both from a decrease in deletions involving the lac operator and an increase in base substitutions involving the i(-d) region in repair proficient organisms. However, elements of the doxorubicin-induced mutation spectrum in uvrB- E. coli are still discernable in wild-type organisms. These elements include the remarkable shift of 3'-deletion endpoints to palindromic sequence within the lac operator and the recovery of multiple isolates of T:A --> A:T transversions at position 96 in doxorubicin-treated cultures. These observations suggest that components of the uvr(A)BC nucleotide excision repair system function through a general mechanism prior to fixation of mutations to reduce, but not completely eliminate, the genotoxic effects of doxorubicin.