Abstract
Expression of the mitochondrial proton-translocating ATPase of Saccharomyces cerevisiae has been shown to depend on chaperones that target the F1 and F0 sectors of this inner membrane complex. Here we report a new gene, designated ATP22 (reading frame YDR350C on chromosome IV), that provides an essential function in the assembly of F0. ATP22 was cloned by transformation of C208/L2, a strain previously assigned to complementation group G99 of a collection of respiration-defective nuclear pet mutants. C208/L2 and the other atp22 mutants have oligomycin-insensitive F1-ATPase, suggesting that the lesion is confined to F0. This is supported by the sedimentation properties of the mutant ATPase and results of immunochemical analysis of F0 subunit polypeptides. Northern analysis of ATPase transcripts and in vivo pulse labeling of the mitochondrial translation products in the mutant indicate normal expression of subunits 6, 8, and 9, the three mitochondrial gene products of F0. Atp22p therefore functions at a post-translational stage in assembly of F0. Localization studies indicate Atp22p to be a component of the mitochondrial inner membrane. Protease protection experiments further indicate that Atp22p faces the matrix side of the membrane where most of the ATPase proteins are located and assembled.
Highlights
Nuclear genes of S. cerevisiae reported previously [12,13,14,15] to affect F0 assembly are involved in processing/translation of the mitochondrial ATPase-specific transcripts for subunits 6, 8, and 9
The ATP22 product reported here is the second example of a mitochondrial protein with a posttranslational role essential for F0 assembly
This is supported by the presence in atp22 mutants of the fully processed ATP6, -8, and -9 mRNAs and their normal translation when cycloheximide-inhibited cells are pulse-labeled with a radioactive precursor
Summary
At least 4 genes have been shown to be required for expression of the mitochondrially encoded subunits 6, 8, and 9 [12,13,14,15] Another nuclear gene, ATP10, codes for a subunit 6-specific chaperone of the inner membrane protein [16]. In continuing efforts to catalogue nuclear gene products that contribute to the maintenance of respiration-competent mitochondria, we have screened the class of pleiotropic pet mutants [17] for defects in ATPase. In this communication we report a new gene ATP22, which is required for the biogenesis of the ATPase. Studies of respiration-deficient yeast mutants have disclosed the existence of at least two nuclear gene products necessary
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