Role of cell wall in Saccharomyces cerevisiae mutants resistant to Hg2+.

Hg2+-resistant mutants were isolated from Saccharomyces cerevisiae. Although they were very much like the parental strains in terms of colony-forming ability, they grew faster than the parental strains in the presence of sublethal doses of Hg2+. The Hg2+-resistant mutations were dominant. They were centromere linked and were divided into two groups by means of recombination; one of the mutations, designated HGR1-1, was mapped on chromosome IV because of its linkage to the TRP1 locus. The Hg2+-resistant mutants took up Hg2+ as much as, or slightly more than, the parental strains did. The mutants and parental strains retained only about 5 and 15%, respectively, of the cell-associated Hg2+ after removal of the cell wall; therefore, the mutants had less spheroplast-associated Hg2+ than did the parental strains. These results indicate that the cell wall plays an important role in protection against Hg2+ by acting as an adsorption filter and that the mutations described confer Hg2+ resistance by increasing the Hg2+-binding capacity of the cell wall.