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, mutants of the yeast Saccharomyces omq,ces cel cerevisiae. Mutations in the GEF1 gene cause cells to grow slowly on rich media containing carbon sources utilized by respiration. This phenotype is suppressed by adding high concentrations of iron to the growth medium. Gef(1-) mutants also fail to grow on a fermentable carbon source, glucose, when iron is reduced to low concentrations in the medium, suggesting that the GEF1 gene is required for efficient metabolism of iron during growth on fermentable as well as respired carbon sources. However, activity of the iron uptake system appears to be unaffected in gef1(-) mutants. Fe(II) transporter activity and regulation is normal in gef1(-) mutants. Fe(III) reductase induction during iron-limited growth is disrupted, but this appears to be a secondary effect of growth rate alterations. The wild-type GEF1 gene was cloned and sequenced; it encodes a protein of 779 amino acids, 13 possible transmembrane domains, and significant similarity to chloride channel proteins from fish and mammals, suggesting that GEF1 encodes an integral membrane protein. A gef1(-) deletion mutation generated in vitro and introduced into wild-type haploid strains by gene transplacement was not lethal. Oxygen consumption by intact gef1(-) cells and by mitochondrial fractions isolated from gef1(-) mutants was reduced 25-50% relative to wild type, indicating that mitochondrial function is defective in these mutants. We suggest that GEF1 encodes a transport protein that is involved in intracellular iron metabolism.