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Vol. 19, Issue 4, 1366-1377, April 2008

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ATP25, a New Nuclear Gene of Saccharomyces cerevisiae Required for Expression and Assembly of the Atp9p Subunit of Mitochondrial ATPase

Department of Biological Sciences, Columbia University, New York, NY 10027

Submitted August 3, 2007; Revised January 3, 2008; Accepted January 15, 2008
Monitoring Editor: Janet Shaw

We report a new nuclear gene, designated ATP25 (reading frame YMR098C on chromosome XIII), required for expression of Atp9p (subunit 9) of the Saccharomyces cerevisiae mitochondrial proton translocating ATPase. Mutations in ATP25 elicit a deficit of ATP9 mRNA and of its translation product, thereby preventing assembly of functional F₀. Unlike Atp9p, the other mitochondrial gene products, including ATPase subunits Atp6p and Atp8p, are synthesized normally in atp25 mutants. Northern analysis of mitochondrial RNAs in an atp25 temperature-sensitive mutant confirmed that Atp25p is required for stability of the ATP9 mRNA. Atp25p is a mitochondrial inner membrane protein with a predicted mass of 70 kDa. The primary translation product of ATP25 is cleaved in vivo after residue 292 to yield a 35-kDa C-terminal polypeptide. The C-terminal half of Atp25p is sufficient to stabilize the ATP9 mRNA and restore synthesis of Atp9p. Growth on respiratory substrates, however, depends on both halves of Atp25p, indicating that the N-terminal half has another function, which we propose to be oligomerization of Atp9p into a proper size ring structure.

* Present address: Department of Microbiology, University of São Paulo, São Paulo, Brazil.

Address correspondence to: Alexander Tzagoloff (spud{at}cubpet.bio.columbia.edu)

Abbreviations used: BN, blue native; mtDNA, mitochondrial DNA; ° mutant, respiratory-deficient mutant lacking mitochondrial DNA; ^–, mutant, respiratory-deficient mutant with a partially deleted mitochondrial genome; PAGE, polyacrylamide gel electrophoresis; pet mutant, respiratory-deficient mutant of yeast with a mutation in a nuclear gene; PCR, polymerase chain reaction; PMSF, phenylmethylsulfonyl fluoride.