title: Preferential targeting of a signal recognition particle-dependent precursor to the Ssh1p translocon in yeast.
abstract: Protein translocation across the endoplasmic reticulum membrane occurs via a "translocon" channel formed by the Sec61p complex. In yeast, two channels exist: the canonical Sec61p channel and a homolog called Ssh1p. Here, we used trapped translocation intermediates to demonstrate that a specific signal recognition particle-dependent substrate, Sec71p, is targeted exclusively to Ssh1p. Strikingly, we found that, in the absence of Ssh1p, precursor could be successfully redirected to 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 reveal a novel sorting mechanism at the level of the endoplasmic reticulum 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.
authors: Faculty of Life Sciences, University of Manchester, M13 9PT Manchester, United Kingdom.
authors: Michael P
authors: MP
authors: Spiller
authors: Colin J
authors: CJ
authors: Stirling
mesh_terms: D004152:Dipeptidyl-Peptidases and Tripeptidyl-Peptidases / Q000378:metabolism; D008565:Membrane Proteins / Q000737:chemistry / Q000378:metabolism*; D017434:Protein Structure, Tertiary; D021381:Protein Transport; D012441:Saccharomyces cerevisiae / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins / Q000737:chemistry / Q000378:metabolism*; D018271:Signal Recognition Particle / Q000378:metabolism*; D013379:Substrate Specificity
chemical_list: D008565:Membrane Proteins; C499381:SSH1 protein, S cerevisiae; D029701:Saccharomyces cerevisiae Proteins; D018271:Signal Recognition Particle; D004152:Dipeptidyl-Peptidases and Tripeptidyl-Peptidases; C059010:dipeptidyl aminopeptidase B