TARGETING AND TRANSLOCATION OF THE PHOSPHATE CARRIER P-32 TO THE INNER MEMBRANE OF YEAST MITOCHONDRIA

We analyzed the submitochondrial location and biogenesis pathway of th e phosphate carrier (P(i)C), also termed p32, of Saccharomyces cerevis iae mitochondria. P(i)C/p32 was found to behave as an integral membran e protein that cofractionated with the ADP/ATP carrier of the inner me mbrane. Import of the precursor of P(i)C/p32 required a membrane poten tial across the inner membrane, supporting its localization to the inn er membrane. This makes it unlikely that the major function of P(i)C/p 32 is that of an import receptor on the surface of the mitochondrial o uter membrane. Furthermore, we found that both receptors MOM72 and MOM 19 were involved in the import pathway of the precursor of P(i)C/p32 w ith MOM72 being responsible for the bulk of import. Yeast P(i)C/p32 is thus not only structurally homologous to the ADP/ATP carrier, but has a similar targeting mechanism and submitochondrial location, supporti ng its classification as a member of the inner membrane carrier family .