Mutants resistant to manganese in Saccharomyces cerevisiae

Several mutants resistant to Mn(2+) have been isolated and characterized in Saccharomyces cerevisiae. All the mutations are semidominant and allelic to a single nuclear gene (MNRI). Mg(2+) in the growth medium reverses the inhibitory effect of Mn(2+) in a competitive way. This appears to be due to the inhibition of the uptake of Mn(2+) by the cells, not to an increase of the amount of Mg(2+) inside the cells.The analysis of the distribution of Mn(2+) 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 Mn(2+) and that the major difference between mutants and wild-type strains lies in the much higher efficiency of this system.