Effect of methanol on the frequency of respiration-deficient mutation induced by ethidium bromide in yeast under growing and non-growing conditions.

The effect of methanol on the frequency of cytoplasmic respiration-deficient (RD) mutation induced by ethidium bromide was investigated in Saccharomyces cerevisiae. When growing cells were treated with ethidium bromide at concentrations higher than 1.0μg/ml, 95 to 100% of surviving cells were RD mutants as judged by the tetrazolium overlay method. The RD mutants induced by 1.0μg/ml ethidium bromide were drastically decreased by addition of 6-8% methanol in both growing and non-growing conditions. Methanol reduced uptake of ethidium bromide by yeast cells, but it did not modify the inhibitory effect of ethidium bromide on in vitro yeast mitochondrial deoxyribonucleic acid synthesis.