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Segregation of the polypeptide translocation apparatus to regions of the endoplasmic reticulum containing ribophorins and ribosomes. I. Functional tests on rat liver microsomal subfractions

A preparation of rat liver microsomes containing 70% of the total cellular endoplasmic reticulum (ER) membranes was subfractionated by isopycnic density centrifugation. Twelve subfractions of different ribosome content ranging in density from 1.06 to 1.29 were obtained and analyzed with respect to m...

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Formato: Texto
Lenguaje:English
Publicado: The Rockefeller University Press 1984
Materias:
Acceso en línea:https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2113578/
https://www.ncbi.nlm.nih.gov/pubmed/6501423
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description A preparation of rat liver microsomes containing 70% of the total cellular endoplasmic reticulum (ER) membranes was subfractionated by isopycnic density centrifugation. Twelve subfractions of different ribosome content ranging in density from 1.06 to 1.29 were obtained and analyzed with respect to marker enzymes, RNA, and protein content, as well as the capacity of these membranes to bind 80S ribosomes in vitro. After removal of native polysomes from these microsomal subfractions by puromycin in a buffer of high ionic strength their capacity to rebind 80S ribosomes approached levels found in the corresponding native membranes before ribosome stripping. This indicates that in vitro rebinding of ribosomes occurs to the same sites occupied in the cell by membrane-bound polysomes. Microsomes in the microsomal subfractions were also tested for their capacity to effect the translocation of nascent secretory proteins into the microsomal lumen utilizing a rabbit reticulocyte translation system programmed with mRNA coding for the precursor of human placental lactogen. Membranes from microsomes with the higher isopycnic density and a high ribosome content showed the highest translocation activity, whereas membranes derived from smooth microsomes had only a very low translocation activity. These results indicate the membranes of the rough and smooth portions of the endoplasmic reticulum are functionally differentiated so that sites for ribosome binding and the translocation of nascent polypeptides are segregated to the rough domain of the organelle.
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spelling pubmed-21135782008-05-01 Segregation of the polypeptide translocation apparatus to regions of the endoplasmic reticulum containing ribophorins and ribosomes. I. Functional tests on rat liver microsomal subfractions J Cell Biol Articles A preparation of rat liver microsomes containing 70% of the total cellular endoplasmic reticulum (ER) membranes was subfractionated by isopycnic density centrifugation. Twelve subfractions of different ribosome content ranging in density from 1.06 to 1.29 were obtained and analyzed with respect to marker enzymes, RNA, and protein content, as well as the capacity of these membranes to bind 80S ribosomes in vitro. After removal of native polysomes from these microsomal subfractions by puromycin in a buffer of high ionic strength their capacity to rebind 80S ribosomes approached levels found in the corresponding native membranes before ribosome stripping. This indicates that in vitro rebinding of ribosomes occurs to the same sites occupied in the cell by membrane-bound polysomes. Microsomes in the microsomal subfractions were also tested for their capacity to effect the translocation of nascent secretory proteins into the microsomal lumen utilizing a rabbit reticulocyte translation system programmed with mRNA coding for the precursor of human placental lactogen. Membranes from microsomes with the higher isopycnic density and a high ribosome content showed the highest translocation activity, whereas membranes derived from smooth microsomes had only a very low translocation activity. These results indicate the membranes of the rough and smooth portions of the endoplasmic reticulum are functionally differentiated so that sites for ribosome binding and the translocation of nascent polypeptides are segregated to the rough domain of the organelle. The Rockefeller University Press 1984-12-01 /pmc/articles/PMC2113578/ /pubmed/6501423 Text en This article is distributed under the terms of an Attribution–Noncommercial–Share Alike–No Mirror Sites license for the first six months after the publication date (see http://www.rupress.org/terms). After six months it is available under a Creative Commons License (Attribution–Noncommercial–Share Alike 4.0 Unported license, as described at http://creativecommons.org/licenses/by-nc-sa/4.0/).
spellingShingle Articles
Segregation of the polypeptide translocation apparatus to regions of the endoplasmic reticulum containing ribophorins and ribosomes. I. Functional tests on rat liver microsomal subfractions
title Segregation of the polypeptide translocation apparatus to regions of the endoplasmic reticulum containing ribophorins and ribosomes. I. Functional tests on rat liver microsomal subfractions
title_full Segregation of the polypeptide translocation apparatus to regions of the endoplasmic reticulum containing ribophorins and ribosomes. I. Functional tests on rat liver microsomal subfractions
title_fullStr Segregation of the polypeptide translocation apparatus to regions of the endoplasmic reticulum containing ribophorins and ribosomes. I. Functional tests on rat liver microsomal subfractions
title_full_unstemmed Segregation of the polypeptide translocation apparatus to regions of the endoplasmic reticulum containing ribophorins and ribosomes. I. Functional tests on rat liver microsomal subfractions
title_short Segregation of the polypeptide translocation apparatus to regions of the endoplasmic reticulum containing ribophorins and ribosomes. I. Functional tests on rat liver microsomal subfractions
title_sort segregation of the polypeptide translocation apparatus to regions of the endoplasmic reticulum containing ribophorins and ribosomes. i. functional tests on rat liver microsomal subfractions
topic Articles
url https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2113578/
https://www.ncbi.nlm.nih.gov/pubmed/6501423