Identification of a third yeast mitochondrial Tom protein with tetratrico peptide repeats

The mitochondrial outer membrane contains a protein complex with at least eight subunits responsible for recognition and translocation of preproteins synthesized in the cytosol. Two subunits, the receptors Tom20 and Tom70, contain tetratrico peptide repeats that are thought to be involved in protein-protein interactions. We have identified Saccharomyces cerevisiae Tom72, a new Tom protein expressed at a low level. Tom72 is homologous to Tom 70, including seven tetratrico peptide repeats. Tom72 is targeted to the mitochondrial outer membrane, forms a large domain exposed to the cytosol and loosely associates with the translocase complex of the outer membrane. These results suggest that Tom72 represents a ninth, weakly expressed component of the preprotein translocase of the mitochondrial outer membrane.