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Published online 28 May 2001. doi:10.1083/jcb.153.5.1061
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© The Rockefeller University Press, 0021-9525/2001//1061 $5.00
The Journal of Cell Biology, Volume 153, Number 5, , 2001 1061-1070

Original Article

Molecular Chaperones in the Yeast Endoplasmic Reticulum Maintain the Solubility of Proteins for Retrotranslocation and Degradation



Shuh-ichi Nishikawaa, Sheara W. Fewellb, Yoshihito Katoa, Jeffrey L. Brodskyb, and Toshiya Endoa

a Department of Chemistry, Graduate School of Science, Nagoya University, Chikusa-ku, Nagoya 464-8602, Japan
b Department of Biological Sciences, University of Pittsburgh, Pittsburgh, Pennsylvania 15260
Department of Chemistry, Graduate School of Science, Nagoya University, Chikusa-ku, Nagoya 464-8602, Japan.81 (52) 789 294781 (52) 789 2490

endo{at}biochem.chem.nagoya-u.ac.jp

Endoplasmic reticulum (ER)-associated degradation (ERAD) is the process by which aberrant proteins in the ER lumen are exported back to the cytosol and degraded by the proteasome. Although ER molecular chaperones are required for ERAD, their specific role(s) in this process have been ill defined. To understand how one group of interacting lumenal chaperones facilitates ERAD, the fates of pro–{alpha}-factor and a mutant form of carboxypeptidase Y were examined both in vivo and in vitro. We found that these ERAD substrates are stabilized and aggregate in the ER at elevated temperatures when BiP, the lumenal Hsp70 molecular chaperone, is mutated, or when the genes encoding the J domain–containing proteins Jem1p and Scj1p are deleted. In contrast, deletion of JEM1 and SCJ1 had little effect on the ERAD of a membrane protein. These results suggest that one role of the BiP, Jem1p, and Scj1p chaperones is to maintain lumenal ERAD substrates in a retrotranslocation-competent state.

Key Words: Jem1p • BiP • ERAD • molecular chaperone • protein translocation

© 2001 The Rockefeller University Press

Abbreviations used in this paper: CPY, carboxypeptidase Y; ERAD, ER-associated degradation; p{alpha}F, pro–{alpha}-factor; pp{alpha}F, prepro–{alpha}-factor.


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