Aluminum-sensitive mutants of Saccharomyces cerevisiae.

We are developing budding yeast, Saccharomyces cerevisiae, as a genetic system for the study of tolerance to the trivalent aluminum cation (Al3+). We have isolated eight mutants that are more sensitive to Al3+ than the wild type. Each mutant represented a different complementation group. A number of the mutants were pleiotropic, and showed defects in other stress responses, changes in tolerance to other metal cations, or abnormal morphology. Two mutants also showed increased dependence on supplemental Mg2+ and Ca2+. One mutant with a relatively specific sensitivity to Al3+ was chosen for molecular complementation. Normal Al3+ tolerance was restored by expression of the MAP kinase gene SLT2. Strains carrying deletions of the SLT2 gene, or of the gene for the corresponding MAP kinase kinase SLK1, showed sensitivity to Al3+. These results indicate that the SLT2 MAP kinase signal transduction pathway is required for yeast to sense and respond to Al3+ stress.