ATP25, a New Nuclear Gene ofSaccharomyces cerevisiaeRequired for Expression and Assembly of the Atp9p Subunit of Mitochondrial ATPase

Abstract

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 F 0 . 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.

F 1 -dependent translation of mitochondrially encoded Atp6p and Atp8p subunits of yeast ATP synthase

“…This was shown previously for strains deficient Atp6p and Atp9p (6,8) and in the present study for the ⌬atp8 null mutant. Interestingly, in vivo translation assays of ⌬atp4 and ⌬atp14 mutants lacking, respectively, subunits b and h of the peripheral stalk, disclosed a severe reduction of both Atp6p and Atp8p.…”

“…3). Since ATP synthase mutants tend to convert at high frequency to Ϫ and 0 mutants that are deficient in mitochondrial protein synthesis (6,14), the arginine auxotrophy could also have resulted from a loss of mtDNA. This was excluded by the presence of 40-60% of ϩ cells in the cultures (Fig.…”

“…Regulation of organellar gene expression was first demonstrated by studies of the b 6 f complex of Chlamydomonas rheinhardtii chloroplasts (1). Translation of the cytochrome f component on chloroplast ribosomes was shown to depend on its association with subunit IV and cytochrome b 6 , two other subunits of the complex, which unlike cytochrome f, are synthesized on cytoplasmic ribosomes.…”

“…Translation of the cytochrome f component on chloroplast ribosomes was shown to depend on its association with subunit IV and cytochrome b 6 , two other subunits of the complex, which unlike cytochrome f, are synthesized on cytoplasmic ribosomes. This regulatory mechanism, termed ''control by epistasis of synthesis'' (CES), although differing in detail, was shown to operate in the biogenesis of other chloroplast proteins including photosystem II (2).…”

“…Assembly of a catalytically active F 1 oligomer occurs independently of F 0 (4) and entails an initial chaperone-dependent association of the ␣ and ␤ subunits into a hexamer constituting most of the protein mass of F 1 (5). Chaperones also play important roles in assembly of F 0 , having been shown to promote oligomerization of the Atp9p ring (6) and association of the ring with Atp6p (7). Interaction of Atp6p with the Atp9p ring is probably a late assembly event as the resultant complex can cause an unregulated proton leak leading to dissipation of the mitochondrial membrane potential.…”