Energy-dependent processing of cytoplasmically made precursors to mitochondrial proteins.

Abstract

Earlier work showed that mitochondrial proteins synthesized in the cytosol are initially made as larger precursors which are then transferred into the organelles and processed to their mature size in the absence of protein synthesis. Depletion of the mitochondrial matrix ATP in intact yeast [Saccharomyces cerevisiae] spheroplasts by various combinations of inhibitors and mutations prevents the processing of precursors to the 3 largest subunits of the mitochondrial F1-ATPase and 2 subunits of the cytochrome bc1 complex. These polypeptides are all synthesized outside the mitochondria and transported to the mitochondrial matrix or inserted into the mitochondrial inner membrane. In contrast, depletion of the matrix ATP does not inhibit processing of the precursor to cytochrome c peroxidase; this enzyme is located in the mitochondrial intermembrane space which is freely accessible to ATP made in the cytosol. The processing of extramitochondrially made precursors or the transfer of these precursors across the mitochondrial inner membrane is thus dependent on ATP.