Nuclear and cytoplasmic cross-resistance and correlated sensitivity to DNA intercalating drugs in a petite-negative yeast

Abstract

SUMMABYEthidium bromide and acriflavin-resistant mutants of petite-negative yeast Kluyveromyces lactis were prepared. One kind of nuclear mutation (EB E1 ) gave resistance to ethidium bromide and correlated sensitivity towards acriflavin. Another nuclear mutation (EB R2 ) did not affect 'natural' resistance of this yeast towards 15 /IM. acriflavin. Both nuclear mutations mapped at different loci, suggesting lack of linkage. Cytoplasmic mutants resistant to these two drugs were unstable when grown in complete media with dextrose, reverting to a wild-type resistance genotype. When grown in glycerol-containing media these mutants maintained their cytoplasmic drug-resistance conferring factors.

Ethidium bromide uptake and change of fluorescence by petite‐negative yeast mutants resistant to this drug

“…One possibility is that EB is not entering the mutant cell; our experimental data favors this point of view since the uptake of EB in all the mutants is much lower than that in the wild type, when the concentration of this drug does not exceed 100 MM in the incubation medium (figs.1 and 2). The concentrations of EB used for these assays are much higher than those employed for mutant selection and growth [4,5]. Fluorescence changes and uptake of EB in Saccharomyces cerevisiae have been found to be totally dependent on substrate availability and monovalent cation transport [6].…”

“…One cytoplasmic and two different classes of nuclear mutants resistant to EB have been isolated and genetically characterized from the petite-negative yeast Kluyveromyces lactis [4,5] in our laboratory. The uptake and change of fluorescence (P*) of EB using whole cells was studied in wild type and these mutant strains with the purpose of elucidating the mechanism of actions of this drug.…”

“…Significant differences were observed between the wild type and the mutant in their capacity to bind this drug. [5] , this media contained only a small quantity of this substrate to help the growth get started. After 48 hours of growth, approximately 5 g(wet weight) of cells were collected and starved in 100 ml of sterilized 0.05 M potassium phosphate buffer pH 6.8 for 36 hr in a rotary shaker at 3O'C.…”