HTOM34 - A NOVEL TRANSLOCASE FOR THE IMPORT OF PROTEINS INTO HUMAN MITOCHONDRIA

Most mitochondrial proteins are nuclear encoded, synthesized on cytoso lic ribosomes, and imported into the mitochondria. We have Identified and characterized a 309 amino acid human protein with a molecular weig ht of 34 kDa that functions as a subunit of the translocase for the im port of such proteins, hTom34 (34-kDa Translocase of the Outer Mitocho ndrial Membrane) is displayed on the surface of mitochondria and is re sistant to extraction under alkaline conditions. Antibodies raised aga inst hTom34 specifically inhibit in vitro import of the mitochondrial precursor protein preornithine transcarbamylase into mitochondria isol ated from rat liver. Based on trypsin digestion experiments, the recep tor has a large (27 kDa) C-terminal domain exposed to the cytosol. Thi s novel component of the protein import machinery possesses a 62 resid ue motif conserved with the Tom70 family of mitochondrial receptors bu t otherwise appears to have no counterpart so far characterized in the mitochondria of any other species.