What differentiates co-translational and post-translational translocation?
Eukaryotes employ two temporally distinct routes for polypeptide entry into ER differing in timing relative to translation. Co-translational pathway dominates for most secretory proteins and large multi-pass membrane proteins in mammals: signal recognition particle binds signal sequence as soon as it emerges from ribosomal exit tunnel, Alu domain of SRP9/14 slows elongation by competing with elongation factor, SRP receptor SRα-SRβ delivers complex to Sec61, translation resumes pushing chain directly into ER lumen, never exposing large hydrophobic segments to cytosol. Post-translational pathway
Ref: Cross et al., J Cell Biol 201: 2013, Co versus Post-translational Translocation Differences.
