SHY1, the Yeast Homolog of the MammalianSURF-1 Gene, Encodes a Mitochondrial Protein Required for Respiration

C173 and W125 are pet mutants ofSaccharomyces cerevisiae, partially deficient in cytochrome oxidase but with elevated concentrations of cytochrome c. Assays of electron transport chain enzymes indicate that the mutations exert different effects on the terminal respiratory pathway, including an inefficient transfer of electrons between thebc1 and the cytochrome oxidase complexes. A cloned gene capable of restoring respiration in C173/U1 and W125 is identical to reading frame YGR112w of yeast chromosome VII (GenBankZ72897). The encoded protein is homologous to the product of the mammalian SURF-1 gene. In view of the homology, the yeast gene has been designated SHY1 (SurfHomolog of Yeast). An antibody against the carboxyl-terminal half of Shy1p has been used to localize the protein in the inner mitochondrial membrane. Deletion of part ofSHY1 produces a phenotype similar to that of G91 mutants. Disruption of SHY1 at a Bam HI site, located approximately 2/3 of the way into the gene, has no obvious phenotypic consequence. This evidence, together with the ability of a carboxyl-terminal coding sequence starting from the Bam HI site to complement a shy1 mutant, suggests that the Shy1p contains two domains that can be separately expressed to form a functional protein.