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The Signal Sequence Receptor Has a Second Subunit and IsPart of a Translocation Complex in the Endoplasmic Reticulum as Probed by Bifunctional Reagents

Görlich, Dirk ; Prehn, Siegfried ; Hartmann, Enno ; Herz, Joachim ; Otto, Albrecht ; Kraft, Regine ; Wiedmann, Martin ; Knespel, Siegne ; Dobberstein, Bernhard ; Rapoport, Tom A.

In: The Journal of Cell Biology, 111 (1990), Nr. 6. pp. 2283-2294

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Abstract

Bifunctional cross-linking reagents were used to probe the protein environment in the ER membrane of the signal sequence receptor (SSR), a 34-kD integral membrane glycoprotein (Wiedmann, M., T. V. Kurzchalia, E. Hartmarm, and T. A. Rapoport. 1987. Nature [Lond.]. 328:830-833). The proximity of several polypeptides was demonstrated. A 22-kD glycoprotein was identified tightly bound to the 34-kD SSR even after membrane solubilization. The 34-kD polypeptide, now termed otSSR, and the 22-kD polypeptide, the #SSR, represent a heterodimer. We report on the sequence of the/3SSR, its membrane topology, and on the mechanism of its integration into the membrane. Cross-linking also produced dimers of the a-subunit of the SSR indicating that oligomers of the SSR exist in the ER membrane. Various bifunctional cross-linking reagents were used to study the relation to ER membrane proteins of nascent chains of preprolactin and/3-1actamase at different stages of their translocation through the membrane. The predominant cross-linked products obtained in high yields contained the aSSR, indicating in conjunction with previous results that it is a major membrane protein in the neighborhood of translocating nascent chains of secretory proteins. The results support the existence of a translocon, a translocation complex involving the SSR, which constitutes the specific site of protein translocation across the ER membrane.

Item Type: Article
Journal or Publication Title: The Journal of Cell Biology
Volume: 111
Number: 6
Date Deposited: 17. Jun 2008 17:36
Date: 1990
Page Range: pp. 2283-2294
Faculties / Institutes: Service facilities > Center for Molecular Biology Heidelberg
Subjects: 570 Life sciences
Schriftenreihe ID: Works by Bernhard Dobberstein
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