Sa. Broadley et al., Peripheral mitochondrial inner membrane protein, Mss2p, required for export of the mitochondrially coded cox2p C tail in Saccharomyces cerevisiae, MOL CELL B, 21(22), 2001, pp. 7663-7672
Cytochrome oxidase subunit 2 (Cox2p) is synthesized on the matrix side of t
he mitochondrial inner membrane, and its N- and C-terminal domains are expo
rted across the inner membrane by distinct mechanisms. The Saccharomyces ce
revisiae nuclear gene MSS2 was previously shown to be necessary for Cox2p a
ccumulation. We have used pulse-labeling studies and the expression of the
ARG8(m) reporter at the COX2 locus in an mss2 mutant to demonstrate that Ms
s2p is not required for Cox2p synthesis but rather for its accumulation. Mu
tational inactivation of the proteolytic function of the matrix-localized Y
ta10p (Afg3p) AAA-protease partially stabilizes Cox2p in an mss2 mutant but
does not restore assembly of cytochrome oxidase. In the absence of Mss2p,
the Cox2p N terminus is exported, but Cox2p C-terminal export and assembly
of Cox2p into cytochrome oxidase is blocked. Epitope-tagged Mss2p is tightl
y, but peripherally, associated with the inner membrane and protected by it
from externally added proteases. Taken together, these data indicate that
Mss2p plays a role in recognizing the Cox2p C tail in the matrix and promot
ing its export.