THE GEF1 GENE OF SACCHAROMYCES-CEREVISIAE ENCODES AN INTEGRAL MEMBRANE-PROTEIN - MUTATIONS IN WHICH HAVE EFFECTS ON RESPIRATION AND IRON-LIMITED GROWTH

We have isolated a new class of respiration-defective, i.e petite, mut ants of the yeast Saccharomyces omq,ces cel cerevisiae. Mutations in t he GEF1 gene cause cells to grow slowly on rich media containing carbo n sources utilized by respiration. This phenotype is suppressed by add ing high concentrations of iron to the growth medium. Gef(1-) mutants also fail to grow on a fermentable carbon source, glucose, when iron i s reduced to low concentrations in the medium, suggesting that the GEF 1 gene is required for efficient metabolism of iron during growth on f ermentable as well as respired carbon sources. However, activity of th e iron uptake system appears to be unaffected in gef1(-) mutants. Fe(I I) transporter activity and regulation is normal in gef1(-) mutants. F e(III) reductase induction during iron-limited growth is disrupted, bu t this appears to be a secondary effect of growth rate alterations. Th e wild-type GEF1 gene was cloned and sequenced; it encodes a protein o f 779 amino acids, 13 possible transmembrane domains, and significant similarity to chloride channel proteins from fish and mammals, suggest ing that GEF1 encodes an integral membrane protein. A gef1(-) deletion mutation generated in vitro and introduced into wild-type haploid str ains by gene transplacement was not lethal. Oxygen consumption by inta ct gef1(-) cells and by mitochondrial fractions isolated from gef1(-) mutants was reduced 25-50% relative to wild type, indicating that mito chondrial function is defective in these mutants. We suggest that GEF1 encodes a transport protein that is involved in intracellular iron me tabolism.