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Science 31 January 2003:
Vol. 299. no. 5607, p. 627
DOI: 10.1126/science.299.5607.627a
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Proteins destined for the inner membrane of the mitochondrion face several hurdles in traveling from the site of their synthesis, which for most of them is the cytosol, across the outer mitochondrial membrane to reach the inner one. They contain internal peptide sequences, which target them to receptors in the outer membrane, and their hydrophobic membrane-spanning segments (which enable them to function as solute transporters) need to be chaperoned, both to avoid aggregation while awaiting translocation and to allow for unfolding and passage through the import pore. Young et al. show that in mammalian cells the cytosolic chaperones Hsp90 and Hsp70 bind to the mitochondrial import receptor Tom70 (which recognizes the targeting sequences) in order to deliver their charges and to promote subsequent translocation events via the adenosine triphosphatase (ATPase) activity of Hsp90. In yeast, only Hsp70 is used in the equivalent reaction, and its ATPase activity is needed for import. -- SMH

Cell 112, 41 (2003).

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