Role of Sec61alpha in the regulated transfer of the ribosome-nascent chain complex from the signal recognition particle to the translocation channel.
Targeting of ribosome-nascent chain complexes to the translocon in the endoplasmic reticulum is mediated by the concerted action of the signal recognition particle (SRP) and the SRP receptor (SR). Ribosome-stripped microsomes were digested with proteases to sever cytoplasmic domains of SRalpha, SRbeta, TRAM, and the Sec61 complex. We characterized protein translocation intermediates that accumulate when Sec61alpha or SRbeta is inactivated by proteolysis. In the absence of a functional Sec61 complex, dissociation of SRP54 from the signal sequence is blocked. Experiments using SR proteoliposomes confirmed the assembly of a membrane-bound posttargeting intermediate. These results strongly suggest that the Sec61 complex regulates the GTP hydrolysis cycle of the SRP-SR complex at the stage of signal sequence dissociation from SRP54.
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Department of Biochemistry and Molecular Biology, University of Massachusetts Medical School, Worcester 01655-0103, USA.
Raden
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Mandon
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Gilmore
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D000818:Animals; D001692:Biological Transport; D004285:Dogs; D018870:Endoplasmic Reticulum, Rough / Q000378:metabolism*; D006160:Guanosine Triphosphate / Q000378:metabolism; D006868:Hydrolysis; D008562:Membrane Glycoproteins / Q000378:metabolism; D008565:Membrane Proteins / Q000378:metabolism*; D008861:Microsomes / Q000378:metabolism; D008954:Models, Biological; D014176:Protein Biosynthesis; D021382:Protein Sorting Signals / Q000378:metabolism; D018160:Receptors, Cytoplasmic and Nuclear / Q000378:metabolism*; D018000:Receptors, Peptide / Q000378:metabolism*; D012270:Ribosomes / Q000378:metabolism*; D000069816:SEC Translocation Channels; D029701:Saccharomyces cerevisiae Proteins; D018271:Signal Recognition Particle / Q000378:metabolism*
D008562:Membrane Glycoproteins; D008565:Membrane Proteins; D021382:Protein Sorting Signals; D018160:Receptors, Cytoplasmic and Nuclear; D018000:Receptors, Peptide; D000069816:SEC Translocation Channels; C069268:SRP54 protein, S cerevisiae; D029701:Saccharomyces cerevisiae Proteins; D018271:Signal Recognition Particle; C036318:signal peptide receptor; C074282:translocating chain-associating membrane protein (TRAM); D006160:Guanosine Triphosphate