Subunit 8 of Yeast Mitochondrial ATP Synthase: Biochemical Genetics and Membrane Assembly

Subunit 8 is a small integral membrane protein of the proton-translocating F0 sector of the mitochondrial ATP synthase complex. We here review our current understanding of the structure, expression and membrane integration of this protein, which is naturally encoded by the mitochondrial aapl gene in bakers’ yeast Saccharomyces cerevisiae. Genetic, biochemical and immunological analyses of yeast mutants deficient in subunit 8 production have begun to reveal the role of subunit 8 in the assembly and function of the mitochondrial ATPase complex. A recent major advance has been the recoding of the gene encoding subunit 8 to achieve its relocation to the nucleus such that nuclearly encoded subunit 8 can be demonstrated to functionally assemble into the mitochondrial ATPase complex. Further, the expression of subunit 8 in vitro, in the form of a chimaeric precursor bearing an N-terminal cleavable presequence, has permitted study of the import of the protein into isolated mitochondria and its assembly into the enzyme complex. The powerful combination of in vivo and in vitro approaches has now led to the systematic manipulation of subunit 8 using site-directed mutagenesis in order to gain further insight into its structure and function.