Yeast Genetics and Molecular Biology 2000
University of Washington
Seattle, Washington USA
July 2000

Name: Broadley, Sarah
Mailing Address: Molecular Biology and Genetics, Cornell University, 333 Biotech Building, Ithaca, NY 14853, USA
Email Address: sab27@cornell.edu
Phone & FAX numbers: 607-254-4834 & 607-255-6249

#013

Mss2p is a peripheral mitochondrial inner membrane protein required for export of a Cox2p-Arg8p fusion protein and stability of Cox2p.
Sarah Broadley, Christina Demlow, Thomas Fox
Molecular Biology and Genetics, Cornell University, 333 Biotech Building, Ithaca, NY 14853, USA

Cytochrome oxidase subunit 2 (Cox2p) is synthesized on the matrix side of the mitochondrial inner membrane. However, its N- and C-terminal domains are exported across the inner membrane by distinct, but as yet unknown, mechanisms. We have identified a nuclear gene product, Mss2p, that appears to be required for Cox2p C-tail export, and to protect the unexported protein from degradation in the matrix. A previous study reported that an mss2mutant contained normal levels of COX2mRNA, but lacked Cox2p (Simon, et al.: BBA 1228:95, 1995). We have used both pulse-labeling studies, and the expression of the ARG8mreporter fused to COX2,to show that Mss2p is not required for Cox2p synthesis, but rather for accumulation. Mutational inactivation of the proteolytic function of the matrix-localized Afg3p (Yta10p) AAA-protease stabilizes Cox2p in an mss2mutant, but does not restore respiratory growth. In the absence of Mss2p, the Cox2p N-tail is exported, but an Arg8p passenger fused to the Cox2p C-terminus is not. Epitope-tagged Mss2p is tightly, but peripherally, associated with the inner membrane and protected by it from externally added proteases. Interestingly, Mss2p has a TPR-like domain similar to that of the mitochondrial import receptor Tom70p. Taken together, these data suggest that Mss2p plays a role in recognizing the Cox2p C-tail, protecting it from degradation in the matrix and promoting its export.

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