Cell Biology

Separating the Rough from the Smooth

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Science  30 Aug 2002:
Vol. 297, Issue 5586, pp. 1447
DOI: 10.1126/science.297.5586.1447a

The endoplasmic reticulum defines an intracellular compartment that is the entry site for proteins destined for the secretory pathway. Proteins cross into the endoplasmic reticulum via a protein complex known as the translocon and, on the lumenal side, encounter an associated oligosaccharyltransferase, which covalently attaches sugar residues. Nikonov et al. examined the mobility of this assemblage by fluorescently tagging the transferase. Translocon complexes that bound the nascent peptides emerging from actively translating ribosomes diffused sevenfold more slowly as compared to other endoplasmic reticulum proteins. A single messenger RNA molecule can be translated by multiple membrane-docked ribosomes at the same time, and this linkage may contribute to the slow diffusion of translocons and also help demarcate rough (ribosome-coated) and smooth (ribosome-free) endoplasmic reticulum domains. — SMH

J. Cell Biol. 158, 497 (2002).

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