ATP synthase of yeast mitochondria - Isolation of subunit j and disruptionof the ATP18 gene

The subunit composition of the mitochondrial ATP synthase from Saccharomyce s cerevisiae was analyzed using blue native gel electrophoresis and high re solution SDS-polyacrylamide gel electrophoresis, We report here the identif ication of a novel subunit of molecular mass of 6,687 Da, termed subunit j (Su j). An open reading frame of 127 base pairs (ATP18), which encodes for Su j, was identified on chromosome XIII. Su j does not display sequence sim ilarity to ATP synthase subunits from other organisms. Data base searches, however, identified a potential homolog from Schizosaccharomyces pombe with 51% identity to Su j of S. cerevisiae. Su j, a small protein of 59 amino a cid residues, has the characteristics of an integral inner membrane protein with a single transmembrane segment. Deletion of the ATP18 gene encoding S u j led to a strain (Delta su j) completely deficient in oligomycin-sensiti ve ATPase activity and unable to grow on nonfermentable carbon sources. The presence of Su j is required for the stable expression of subunits 6 and f of the F-0 membrane sector. In the absence of Su j, spontaneously arising rho(-) cells were observed that lacked also ubiquinol-cytochrome c reductas e and cytochrome c oxidase activities. We conclude that Su j is a novel and essential subunit of yeast ATP synthase.