Preferential targeting of an SRP-dependent precursor to the Ssh1p translocon in yeast.

Protein translocation across the endoplasmic reticulum (ER) membrane occurs via a "translocon" channel formed by the Sec61p complex. A homologue of Sec61p, called Ssh1p, has been identified in yeast and here we use trapped translocation intermediates to demonstrate that a specific SRP-dependent substrate, Sec71p, is targeted exclusively to Ssh1p. Strikingly, ...
we found that, in the absence of Ssh1p, precursor could be successfully re-directed to the canonical Sec61p demonstrating that the normal targeting reaction must involve preferential sorting to Ssh1p. Our data therefore demonstrate that Ssh1p is the primary translocon for Sec71p and reveals a novel sorting mechanism at the level of the ER membrane enabling precursors to be directed to distinct translocons. Interestingly, the Ssh1p-dependent translocation of Sec71p was found to be dependent upon Sec63p demonstrating a previously unappreciated functional interaction between Sec63p and the Ssh1p translocon.
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Date: Mar. 28, 2011
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