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Molecular and Cellular Biology, July 2007, p. 4664-4673, Vol. 27, No. 13
0270-7306/07/$08.00+0     doi:10.1128/MCB.01955-06
Copyright © 2007, American Society for Microbiology. All Rights Reserved.

Translocation of Mitochondrially Synthesized Cox2 Domains from the Matrix to the Intermembrane Space

Heather L. Fiumera, Sarah A. Broadley, and Thomas D. Fox^*

Department of Molecular Biology and Genetics, Cornell University, Ithaca, New York 14853-2703

Received 17 October 2006/ Returned for modification 22 January 2007/ Accepted 16 April 2007

The N-terminal and C-terminal domains of mitochondrially synthesized cytochrome c oxidase subunit II, Cox2, are translocated through the inner membrane to the intermembrane space (IMS). We investigated the distinct mechanisms of N-tail and C-tail export by analysis of epitope-tagged Cox2 variants encoded in Saccharomyces cerevisiae mitochondrial DNA. Both the N and C termini of a truncated protein lacking the Cox2 C-terminal domain were translocated to the IMS via a pathway dependent upon the conserved translocase Oxa1. The topology of this Cox2 variant, accumulated at steady state, was largely but not completely unaffected in mutants lacking proteins required for export of the C-tail domain, Cox18 and Mss2. C-tail export was blocked by truncation of the last 40 residues from the C-tail domain, indicating that sequence and/or structural features of this domain are required for its translocation. Mss2, a peripheral protein bound to the inner surface of the inner membrane, coimmunoprecipitated with full-length newly synthesized Cox2, whose leader peptide had already been cleaved in the IMS. Our data suggest that the C-tail domain is recognized posttranslationally by a specialized translocation apparatus after the N-tail has been translocated by Oxa1.

Published ahead of print on 23 April 2007.

Present address: Department of Cellular Biochemistry, Max Planck Institute of Biochemistry, 82152 Martinsried, Germany.