The YTA10-12 complex, an AAA protease with chaperone-like activity in the inner membrane of mitochondria.

The mitochondrial members of the highly conserved AAA family, Yta10p and Yta12p, constitute a membrane-embedded complex of about 850 kDa. As an ATP dependent metallopeptidase (AAA protease), the YTA10-12 complex mediates the degradation of nonassembled inner membrane proteins. In contrast to nucleotide-dependent complex formation and substrate binding, proteolysis of bound polypeptides depends on the hydrolysis of ATP and the metallopeptidase activity of both subunits. Independent of its proteolytic function, the chaperone-like activity of the YTA10-12 complex is required for assembly of the membrane-associated ATP synthase. We propose that proteolytic and chaperone-like activities in the YTA10-12 complex mediate assembly and degradation processes of membrane protein complexes and thereby exert key functions in the maintenance of membrane integrity.

Yta10p, a member of a novel ATPase family in yeast, is essential for mitochondrial function.

The yeast gene, YTA10, encodes a member of a novel family of putative ATPases. Yta10p, as deduced from the nucleotide sequence, is 761 amino acids in length (predicted molecular mass 84.5 kDa). The amino acid sequence of Yta10p exhibits high similarity to two other yeast proteins, Yta11 and Yta12, and to E. coli FtsH. Several features of Yta10p are compatible with its localization in mitochondria. We report here that Yta10p is a yeast mitochondrial protein and that import is dependent on a membrane potential and accompanied by processing to a protein of approximately 73 kDa. Disruption of YTA10 leads to a nuclear petite phenotype and to a loss of respiratory competence, as shown by spectrophotometric measurement of the activities of respiratory complexes I-III and IV, respectively. These findings together with the high similarity of Yta10p to several ATP-dependent proteases suggest that Yta10p is a mitochondrial component involved, directly or indirectly, in the correct assembly and/or maintenance of active respiratory complexes.

Yta10p is required for the ATP-dependent degradation of polypeptides in the inner membrane of mitochondria.

Incompletely synthesized polypeptides in the mitochondrial inner membrane are subject to rapid proteolysis. We demonstrate that Yta10p, a mitochondrial homologue of a conserved family of putative ATPases in Saccharomyces cerevisiae, is essential for this proteolytic process. Yta10p-dependent degradation requires divalent metal ions and the hydrolysis of ATP. Yta10p is an integral protein of the inner mitochondrial membrane exposing the carboxy terminus to the mitochondrial matrix space. Based on the presence of consensus binding sites for ATP, and for divalent metal ions found in a number of metal dependent endopeptidases, a direct role of Yta10p in the proteolytic breakdown of membrane-associated polypeptides in mitochondria is suggested.

Identification of a set of yeast genes coding for a novel family of putative ATPases with high similarity to constituents of the 26S protease complex.

There is accumulating evidence for a large, highly conserved gene family of putative ATPases. We have identified 12 different members of this novel gene family (the YTA family) in yeast and determined the nucleotide sequences of nine of these genes. All of the putative gene products are characterized by the presence of a highly conserved domain of 300 amino acids containing specialized forms of the A and B boxes of ATPases. YTA1, YTA2, YTA3 and YTA5 exhibit significant similarity to proteins involved in human immunodeficiency virus Tat-mediated gene expression but more significantly to subunits of the human 26S proteasome. YTA1 and YTA2 are essential genes in yeast. Remarkably, the cDNA of human TBP-1 can compensate for the loss of YTA1. Preliminary experiments indicate that YTA1 is a component of the 26S protease complex from yeast. Our findings lead us to propose that YTA1, YTA2, YTA3 and YTA5 function as regulatory subunits of the yeast 26S proteasome. YTA10, YTA11 and YTA12 share significant homology with the Escherichia coli FtsH protein, and together with YTA4 and YTA6 may constitute a separate subclass within this family of putative ATPases.