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Letters to Nature

Nature 424, 565-571 (31 July 2003) | doi:10.1038/nature01753; Received 19 April 2003; Accepted 7 May 2003

Machinery for protein sorting and assembly in the mitochondrial outer membrane

Nils Wiedemann1,2, Vera Kozjak1,2, Agnieszka Chacinska1, Birgit Schönfisch1, Sabine Rospert3, Michael T. Ryan1,4, Nikolaus Pfanner1 & Chris Meisinger1

  1. Institut für Biochemie und Molekularbiologie, Universität Freiburg, Hermann-Herder-Str. 7, D-79104 Freiburg, Germany
  2. Fakultät für Biologie, Universität Freiburg, D-79104 Freiburg, Germany
  3. Max-Planck Research Unit Enzymology of Protein Folding, Weinbergweg 22, D-06120 Halle, Saale, Germany
  4. Present address: Department of Biochemistry, La Trobe University, 3086 Melbourne, Australia

Correspondence to: Nils Wiedemann1,2 Email: Nikolaus.Pfanner@biochemie.uni-freiburg.de

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Mitochondria contain translocases for the transport of precursor proteins across their outer and inner membranes1, 2, 3, 4, 5. It has been assumed that the translocases also mediate the sorting of proteins to their submitochondrial destination1, 2, 5, 6, 7, 8, 9, 10. Here we show that the mitochondrial outer membrane contains a separate sorting and assembly machinery (SAM) that operates after the translocase of the outer membrane (TOM). Mas37 forms a constituent of the SAM complex. The central role of the SAM complex in the sorting and assembly pathway of outer membrane proteins explains the various pleiotropic functions that have been ascribed to Mas37 (refs 4, 11–15). These results suggest that the TOM complex, which can transport all kinds of mitochondrial precursor proteins, is not sufficient for the correct integration of outer membrane proteins with a complicated topology, and instead transfers precursor proteins to the SAM complex.