Identification of SLF1 as a New Copper Homeostasis Gene Involved in Copper Sulfide Mineralization in Saccharomyces cerevisiae

Abstract

In Saccharomyces cerevisiae, at least 12 genes are important for cells to propagate in medium containing elevated concentrations of copper salts (J. Welch, S. Fogel, C. Buchman, and M. Karin, EMBO J. 8:255–260, 1989). Complementation studies were carried out on a copper-sensitive mutation (cup14) from this group. A new yeast gene, designated SLF1, was identified as a multicopy suppressor of the cup14 mutation. Slf1 is important for the physiological process of copper sulfide (CuS) mineralization on the surface of cells cultured in medium containing copper salts. CuS mineralization causes the cells to turn brown. Disruption of SLF1, which is located close to the telomere region of chromosome IV, leads to limited copper sensitivity, and the resulting cells lack the normal brownish coloration when grown in CuSO₄-containing medium. Overproduction of Slf1 in wild-type cells confers superresistance to CuSO₄ and enhances the coloration of cells cultured in the presence of CuSO₄. Upon addition of KCN to Cu-grown cells, the brownish coloration was bleached instantly, and copper ions were solubilized. These data are consistent with Slf1-dependent accumulation of CuS complexes on the cell surface. Disruption of SLF1 also results in loss of the ability of yeast cells to deplete Cu but not Cd ions from the growth medium, whereas overexpression enhances Cu depletion ability and the resulting deposition of CuS particles. It is proposed that Slf1 participates in a copper homeostasis pathway, distinct from the Cup1 detoxification system, that leads to sulfide generation and CuS biomineralization on the cell surface. This process may coordinate with the Cup1 pathway at different copper concentrations to prevent copper-induced toxicity.