PathwayStep413 PathwayStep415 PathwayStep414 PathwayStep417 PathwayStep416 Synthesis of nascent polypeptide containing signal sequence Association of a nascent polypeptide:mRNA:ribosome complex with a signal recognition particle (SRP) Signal peptide cleavage from ribosome-associated nascent protein Translocation of signal-containing nascent peptide to Endoplasmic Reticulum The SRP receptor binds the SRP:nascent peptide:ribosome complex SRP-dependent cotranslational protein targeting to membrane Authored: May, B, Gopinathrao, G, 2008-11-19 19:22:37 Edited: D'Eustachio, P, 2011-10-23 GENE ONTOLOGYGO:0006614 Reactome Database ID Release 431799339 Reactome, http://www.reactome.org ReactomeREACT_115902 Reviewed: D'Eustachio, P, Matthews, L, Gillespie, ME, 2008-12-02 16:25:31 The process for translation of a protein destined for the endoplasmic reticulum (ER) branches from the canonical cytoslic translation process at the point when a nascent polypeptide containing a hydrophobic signal sequence is exposed on the surface of the cytosolic ribosome:mRNA:peptide complex. The signal sequence mediates the interaction of this complex with a cytosolic signal recognition particle (SRP) to form a complex which in turn docks with an SRP receptor complex on the ER membrane. There the ribosome complex is transferred from the SRP complex to a translocon complex embedded in the ER membrane and reoriented so that the nascent polypeptide protrudes through a pore in the translocon into the ER lumen. Translation, which had been halted by SRP binding, now resumes, the signal peptide is cleaved from the polypeptide, and elongation proceeds, with the growing polypeptide oriented into the ER lumen.