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

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

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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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