SACCHAROMYCES-CEREVISIAE MUTANTS ALTERED IN VACUOLE FUNCTION ARE DEFECTIVE IN COPPER DETOXIFICATION AND IRON-RESPONSIVE GENE-TRANSCRIPTION

The metal ions, Cu2+/+ and Fe3+/2+, are essential co-factors for a wid e variety of enzymatic reactions, However, both metal ions are toxic w hen hyper-accumulated or maldistributed within cells due to their abil ity to generate damaging free radicals or through the displacement of ether physiological metal ions from metalloproteins. Although copper t ransport into yeast cells is apparently independent of iron, the known dependence on Cu2+ for high affinity transport of Fe2+ into yeast cel ls has established a physiological link between these two trace metal ions. In this study we demonstrate that proteins encoded by genes prev iously demonstrated to play critical roles in vacuole assembly or acid ification, PEP3, PEPS and VMA3, are also required for normal copper an d iron metal ion homeostasis. Yeast cells lacking a functional PEP3 or PEPS gene are hypersensitive to copper and render the normally iron-r epressible FET3 gene, encoding a multi-copper Fe(II) oxidase involved if Fe2+ transport, also repressible by exogenous copper ions. The inab ility of these sams vacuolar mutant strains to repress FET3 mRNA level s in the presence of an iron-unresponsive allele of the AFT1 regulator y gene are consistent with alterations in the intracellular distributi on or redox states of Fe3+/2+ in the presence of elevated extracellula r concentrations of copper ions. Therefore, the yeast vacuole is an im portant organelle for maintaining the homeostatic convergence of the e ssential yet toxic copper and iron ions. (C) 1997 John Wiley & Sons, L td.