Oxa1p, which is required for cytochrome c oxidase and ATP synthase complex formation, is embedded in the mitochondrial inner membrane

We have previously isolated the yeast nuclear gene OXA1 and showed that Oxa1p is required for the formation of the cytochrome c oxidase and ATP synthase complexes, We have expressed Oxa1p in E. coli and shown that it is toxic and rapidly degraded. Nevertheless, a truncated protein was successfully expressed and antibodies have been raised against this truncated protein. These antibodies recognise a protein in mitochondrially enriched fractions. In vitro mitochondrial import experiments demonstrate that the import of Oxa1p is accompanied by the cleavage of a long pre-sequence. Osmotic swelling and alkaline carbonate extraction show that Oxa1p is an integral membrane protein located in the inner membrane of mitochondria. The relationships between the sub-mitochondrial location and the function of Oxa1p are discussed.