Bleomycin belongs to a class of antitumor drugs that damage cellular DNA through the production of free radicals. The molecular basis by which eukaryotic cells provide resistance to the lethal effects of bleomycin is not clear. Using the yeast Saccharomyces cerevisiae as a model with which to study the effect of bleomycin damage on cellular DNA, we isolated several mutants that display hypersensitivity to bleomycin. A DNA clone containing the IMP2 gene that complemented the most sensitive bleomycin mutant was identified. A role for IMP2 in defense against the toxic effects of bleomycin has not been previously reported. imp2 null mutants were constructed and were found to be 15-fold more sensitive to bleomycin than wild-type strains. The imp2 null mutants were also hypersensitive to several oxidants but displayed parental resistance to UV light and methyl methane sulfonate. Exposure of mutants to either bleomycin or hydrogen peroxide resulted in the accumulation of strand breaks in the chromosomal DNA, which remained even after 6 h postchallenge, but not in the wild type. These results suggest that the oxidant hypersensitivity of the imp2 mutant results from a defect in the repair of oxidative DNA lesions. Molecular analysis of IMP2 indicates that it encodes a transcriptional activator that can activate a reporter gene via an acidic domain located at the N terminus. Imp2 lacks a DNA binding motif, but it possesses a C-terminal leucine-rich repeat. With these data taken together, we propose that Imp2 prevents oxidative damage by regulating the expression of genes that are directly required to repair DNA damage.