A NEW MEMBER OF A FAMILY OF ATPASES IS ESSENTIAL FOR ASSEMBLY OF MITOCHONDRIAL RESPIRATORY-CHAIN AND ATP-SYNTHETASE COMPLEXES IN SACCHAROMYCES-CEREVISIAE

Respiration-defective pet mutants of Saccharomyces cerevisiae, assigne d to complementation group G25, are grossly deficient in mitochondrial respiratory and ATPase complexes. This phenotype is usually found in strains impaired in mitochondrial protein synthesis. The G25 mutants, however, synthesize all of the proteins encoded by mitochondrial DNA. The mutants are also able to import and process cytoplasmically derive d subunits of these enzymes. These results are most compatible with th e idea that the gene defined by G25 mutants (RCA1) codes for a protein essential for the assembly of functional respiratory and ATPase compl exes. The RCA1 gene has been cloned by complementation of an rca1 muta nt with a yeast genomic library. The sequence of the encoded product s hows Rca1 protein to be a new member of a recently described family of ATPases. The Rca1 protein is a mitochondrial membrane protein and is the third known member of this family implicated to function in the bi ogenesis of mitochondria. The primary structure of Rca1 protein indica tes several distinct domains in addition to the common purine nucleoti de binding region shared by all members of this protein family. One, l ocated in the amino-terminal half, contains two hydrophobic stretches of sufficient length to span a membrane lipid bilayer.