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Binding of ribosomes to the rough endoplasmic reticulum mediated by the sec61p-complex

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Item Type:Article
Title:Binding of ribosomes to the rough endoplasmic reticulum mediated by the sec61p-complex
Creators Name:Kalies, K.U. and Goerlich, D. and Rapoport, T.A.
Abstract:The cotranslational translocation of proteins across the ER membrane involves the tight binding of translating ribosomes to the membrane, presumably to ribosome receptors. The identity of the latter has been controversial. One putative receptor candidate is Sec61 alpha, a multi-spanning membrane protein that is associated with two additional membrane proteins (Sec61 beta and gamma) to form the Sec61p-complex. Other receptors of 34 and 180 kD have also been proposed on the basis of their ability to bind at low salt concentration ribosomes lacking nascent chains. We now show that the Sec61p-complex has also binding activity but that, at low salt conditions, it accounts for only one third of the total binding sites in proteoliposomes reconstituted from a detergent extract of ER membranes. Under these conditions, the assay has also limited specificity with respect to ribosomes. However, if the ribosome-binding assay is performed at physiological salt concentration, most of the unspecific binding is lost; the Sec61p-complex then accounts for the majority of specific ribosome-binding sites in reconstituted ER membranes. To study the membrane interaction of ribosomes participating in protein translocation, native rough microsomes were treated with proteases. The amount of membrane-bound ribosomes is only slightly reduced by protease treatment, consistent with the protease-resistance of Sec61 alpha which is shielded by these ribosomes. In contrast, p34 and p180 can be readily degraded, indicating that they are not essential for the membrane anchoring of ribosomes in protease-treated microsomes. These data provide further evidence that the Sec61p-complex is responsible for the membrane-anchoring of ribosomes during translocation and make it unlikely that p34 or p180 are essential for this process.
Keywords:DNA, Endoplasmic Reticulum, Genetic Transcription, Kinetics, Liposomes, Membrane Fusion, Membrane Proteins, Messenger RNA, Microsomes, Pancreas, Post-Translational Protein Processing, Prolactin, Protein Biosynthesis, Protein Precursors, Proteolipids, Ribosomes, Animals, Dogs
Source:Journal of Cell Biology
Publisher:Rockefeller University Press
Page Range:925-934
Date:August 1994
Additional Information:Copyright (c) 1994 by The Rockefeller University Press
Official Publication:http://www.jcb.org/cgi/content/abstract/126/4/925
PubMed:View item in PubMed

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