title: Formation of an energized inner membrane in mitochondria with a gamma-deficient F1-ATPase.
abstract: Eukaryotic cells require mitochondrial compartments for viability. However, the budding yeast Saccharomyces cerevisiae is able to survive when mitochondrial DNA suffers substantial deletions or is completely absent, so long as a sufficient mitochondrial inner membrane potential is generated. In the absence of functional mitochondrial DNA, and consequently a functional electron transport chain and F(1)F(o)-ATPase, the essential electrical potential is maintained by the electrogenic exchange of ATP(4-) for ADP(3-) through the adenine nucleotide translocator. An essential aspect of this electrogenic process is the conversion of ATP(4-) to ADP(3-) in the mitochondrial matrix, and the nuclear-encoded subunits of F(1)-ATPase are hypothesized to be required for this process in vivo. Deletion of ATP3, the structural gene for the gamma subunit of the F(1)-ATPase, causes yeast to quantitatively lose mitochondrial DNA and grow extremely slowly, presumably by interfering with the generation of an energized inner membrane. A spontaneous suppressor of this slow-growth phenotype was found to convert a conserved glycine to serine in the beta subunit of F(1)-ATPase (atp2-227). This mutation allowed substantial ATP hydrolysis by the F(1)-ATPase even in the absence of the gamma subunit, enabling yeast to generate a twofold greater inner membrane potential in response to ATP compared to mitochondria isolated from yeast lacking the gamma subunit and containing wild-type beta subunits. Analysis of the suppressing mutation by blue native polyacrylamide gel electrophoresis also revealed that the alpha(3)beta(3) heterohexamer can form in the absence of the gamma subunit.
authors.affiliation: Department of Molecular Biology, University of Wyoming, Laramie, WY 82071, USA.
authors.forename: Christopher P
authors.initials: CP
authors.lastname: Smith
authors.forename: Peter E
authors.initials: PE
authors.lastname: Thorsness
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D000483:Alleles; D000595:Amino Acid Sequence; D019943:Amino Acid Substitution; D000818:Animals; D002417:Cattle; D017124:Conserved Sequence; D004272:DNA, Mitochondrial / Q000235:genetics; D004591:Electrophoresis, Polyacrylamide Gel; D017353:Gene Deletion; D005800:Genes, Fungal; D016153:Genes, Suppressor; D006868:Hydrolysis; D007425:Intracellular Membranes / Q000502:physiology*; D008564:Membrane Potentials; D008928:Mitochondria / Q000502:physiology*; D000226:Mitochondrial ADP, ATP Translocases / Q000235:genetics / Q000378:metabolism; D008958:Models, Molecular; D008968:Molecular Conformation; D008969:Molecular Sequence Data; D021122:Protein Subunits / Q000737:chemistry / Q000235:genetics; D006180:Proton-Translocating ATPases / Q000172:deficiency / Q000235:genetics*; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000254:growth & development; D012694:Serine / Q000378:metabolism
chemical_list: D004272:DNA, Mitochondrial; D021122:Protein Subunits; D012694:Serine; D000255:Adenosine Triphosphate; D000226:Mitochondrial ADP, ATP Translocases; D006180:Proton-Translocating ATPases