Abstract
Mechanism of Polypeptide Translocation into the Endoplasmic Reticulum
Highlights
Two pathways of targeting to the endoplasmic reticulum (ER) are known
SRP54 binds to the signal sequence as it emerges from the ribosome, probably through a direct interaction with the hydrophobic domain of the signal sequence [6, 7] (Fig. 1a)
The SRP receptor (SR) components, as well as SRP54, have GTP binding domains suggesting that GTP hydrolysis may aid in the regulation of targeting [6, 7]
Summary
All polypeptides destined for transit through the secretory pathway begin their journey by crossing the endoplasmic reticulum (ER) membrane, whether their final destination is the ER lumen or membrane, the Golgi apparatus, the vacuole or lysosome, the plasma membrane, or the extracellular milieu. This translocation step presents eukaryotic cells with a number of problems. Once precursors arrive at the ER membrane, they must engage the integral or peripherally associated membrane proteins of the translocation apparatus (or translocon) that directly aid in protein import. We describe a number of recent observations that help to create an emerging picture of the initial step of protein secretion (for recent reviews, see Refs. 1–3)
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