Chromium resistant mutants of the yeast Saccharomyces cerevisiae

Many strains of Saccharomyces cerevisiae do not grow on YPD agar containing 750 μg/ml CrO3. Mutants able to grow in the presence of 850 μg/ml CrO3 were obtained from such strains after UV mutagenesis. All of the mutants grew even in the presence of 1,000 μ/ml CrO3. Chromium resistance was dominant or partial dominant over normal response, therefore it was impossible to determine the number of genetic loci by complementation analysis. However, the segregation of representative mutants strongly indicated that resistance was determined by single mutations. In addition, a limited analysis of recombination suggested that the chromium resistant mutations were located on a certain region of the yeast genome. Although it was determined that the mutants had slightly reduced rates of Cr(6+) uptake, the exact mechanism of resistance was not discovered. According to the studies of interactions between resistant mutations and sensitive mutations, however, we have proposed a preliminary pathway of Cr(6+) detoxification.