Mutants resistant to manganese in Saccharomyces cerevisiae

Summary Several mutants resistant to Mn²⁺ have been isolated and characterized in Saccharomyces cerevisiae. All the mutations are semidominant and allelic to a single nuclear gene (MNRI). Mg²⁺ in the growth medium reverses the inhibitory effect of Mn²⁺ in a competitive way. This appears to be due to the inhibition of the uptake of Mn²⁺ by the cells, not to an increase of the amount of Mg²⁺ inside the cells.The analysis of the distribution of Mn²⁺ taken up by growing cells shows that the amount of the ion present in insoluble form is far higher in resistant than in sensitive cells. We therefore believe that yeast cells have a sequestering system for Mn²⁺ and that the major difference between mutants and wild-type strains lies in the much higher efficiency of this system.