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A more recent version of this article appeared on September 1, 2006
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Submitted on March 14, 2006
Revised on June 8, 2006
Accepted on June 22, 2006
Biozentrum, University of Basel, CH-4056 Basel, Switzerland
Monitoring Editor: Reid Gilmore
The Sec61/SecY translocon mediates translocation of proteins across the membrane and integration of membrane proteins into the lipid bilayer. The structure of the translocon revealed a plug domain blocking the pore on the lumenal side. It was proposed to be important for gating the protein conducting channel and to maintain the permeability barrier in its unoccupied state. Here we analyzed in yeast the effect of introducing destabilizing point mutations in the plug domain or of its partial or complete deletion. Unexpectedly, even when the entire plug domain was deleted, cells were viable without growth phenotype. They showed an effect on signal sequence orientation of diagnostic signal-anchor proteins, a minor defect in cotranslational and a significant deficiency in post-translational translocation. Steady-state levels of the mutant protein were reduced, and when coexpressed with wild-type Sec61p, the mutant lacking the plug competed poorly for complex partners. The results suggest that the plug is unlikely to be important for sealing the translocation pore in yeast, but that it plays a role in stabilizing Sec61p during translocon formation.
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