Isolation of supernumerary yeast ATP synthase subunits e and i. Characterization of subunit i and disruption of its structural gene ATP18.
Two subunits of the yeast ATP synthase have been isolated. Subunit e was found loosely associated to the complex. Triton X-100 at a 1% concentration removed this subunit from the ATP synthase. The N-terminal sequencing of subunit i has been performed. The data are in agreement with the sequence of the predicted product of a DNA fragment of Saccharomyces cerevisiae chromosome XIII. The ATP18 gene encodes subunit i, which is 59 amino acids long and corresponds to a calculated mass of 6687 Da. Its pI is 9.73. It is an amphiphilic protein having a hydrophobic N-terminal part and a hydrophilic C-terminal part. It is not apparently related to any subunit described in other ATP synthases. The null mutant showed low growth on nonfermentable medium. Mutant mitochondria display a low ADP/O ratio and a decrease with time in proton pumping after ATP addition. Subunit i is associated with the complex; it is not a structural component of the enzyme but rather is involved in the oxidative phosphorylations. Similar amounts of ATP synthase were measured for wild-type and null mutant mitochondria. Because 2-fold less specific ATPase activity was measured for the null mutant than for the wild-type mitochondria, we make the hypothesis that the observed decrease in the turnover of the mutant enzyme could be linked to a proton translocation defect through F0.
Vaillier
J
J
Institut de Biochimie et Génétique Cellulaires du CNRS, Université Victor Ségalen, Bordeaux 2, 33077 Bordeaux cedex, France.
Arselin
G
G
Graves
P V
PV
Camougrand
N
N
Velours
J
J
D000595:Amino Acid Sequence; D001483:Base Sequence; D004271:DNA, Fungal; D005800:Genes, Fungal; D008969:Molecular Sequence Data; D009154:Mutation; D010085:Oxidative Phosphorylation; D010641:Phenotype; D006180:Proton-Translocating ATPases / Q000235:genetics / Q000302:isolation & purification* / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000201:enzymology* / Q000235:genetics
D004271:DNA, Fungal; D006180:Proton-Translocating ATPases