Targeting of proteins to mitochondria

A clear picture has emerged over the past years on how a 'classic' mitochon drial protein, like subunit IV of cytochrome c oxidase, might be targeted t o mitochondria. The targeting and subsequent import process involves the co mmitment of the TOM (translocase in the outer mitochondrial membrane) recep tor complex on the mitochondrial surface, a TIM translocase in the inner mi tochondrial membrane) translocation complex in the mitochondrial inner memb rane, and assorted chaperones and processing enzymes within the organelle. Recent work suggests that while very many mitochondrial precursor proteins might follow this basic targeting pathway, a large number have further requ irements if they are to be successfully imported. These include ribosome-as sociated factors and soluble factors in the cytosol, soluble factors in the mitochondrial intermembrane space, an additional TIM translocase in the in ner membrane and a range of narrow specificity assembly factors in the inne r membrane. This review is focused on the targeting of proteins up to the s tage at which they enter the TOM complex in the outer membrane, (C) 2000 Fe deration of European Biochemical Societies. Published by Elsevier Science B .V. All rights reserved.