Effects of Methanol and Magnesium Chloride on the Induction of Respiration-Deficient Mutants in Yeast by Metal Ions

Abstract

The effects of methanol and magnesium chloride on the induction of cytoplasmic respirationdeficient (RD or petite) mutants of yeast, Saccharomyces cerevisiae, by metal compounds were investigated. ZnCl₂, HgCl₂, NiCl₂, CdCl₂ and MnCl₂ induced 1.8-2.2% RD mutants at concentrations where almost no growth inhibition was observed. Induction of RD mutants by these metal compounds decreased to the spontaneous level (1.4%) in 4% methanol. The effect of methanol was weaker on RD mutant induction by PbCl₂ and CuCl₂. The induction of RD mutants by CoCl₂ was not affected by methanol. NiCl₂ and CdCl₂ were strongly mutagenic at higher concentrations, and the mutagenicity of these metal compounds was also repressed by 4% methanol. The frequency of RD mutants induced in the presence of 1×10^-2M MnCl₂ was increased from 13.5 to 60.7% by the addition of methanol. This increase of the induction of RD mutants in the presence of MnCl₂ and methanol was antagonized almost completely by the addition of MgCl₂ to the culture medium. The same effect of MgCl₂ was observed in the absence of methanol. The effects of methanol and MgCl₂ on the induction of RD mutants in yeast are discussed.