Article
- The EMBO Journal (2008) 27, 2204 - 2213
- doi:10.1038/emboj.2008.148
Published online: 24 July 2008
Subject Category:
Dissecting 
-ring assembly pathway of the mammalian 20S proteasome
Yuko Hirano1, Takeumi Kaneko2, Kenta Okamoto3, Minghui Bai2, Hideki Yashiroda2, Kaori Furuyama2, Koichi Kato3,4, Keiji Tanaka1 and Shigeo Murata2
- Laboratory of Frontier Science, Tokyo Metropolitan Institute of Medical Science, Tokyo, Japan
- Laboratory of Protein Metabolism, Department of Integrated Biology, Graduate School of Pharmaceutical Sciences, The University of Tokyo, Tokyo, Japan
- Department of Structural Biology and Biomolecular Engineering, Graduate School of Pharmaceutical Sciences, Nagoya City University, Nagoya, Japan
- Division of Biomolecular Functions, Department of Life and Coordination-Complex Molecular Science, Institute for Molecular Science, National Institutes of Natural Sciences, Okazaki, Japan
Correspondence to:
Shigeo Murata, Laboratory of Protein Metabolism, Department of Integrated Biology, Graduate School of Pharmaceutical Sciences, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan. Tel.: +81 3 5841 4803; Fax: +81 3 5841 4805; E-mail: smurata@mol.f.u-tokyo.ac.jp
Received 14 April 2008; Accepted 3 July 2008
Abstract
The 20S proteasome is the catalytic core of the 26S proteasome. It comprises four stacked rings of seven subunits each, 
1–7
1–71–71–7. Recent studies indicated that proteasome-specific chaperones and -subunit appendages assist in the formation of -rings and dimerization of half-proteasomes, but the process involved in the assembly of -rings is poorly understood. Here, we clarify the mechanism of -ring formation on -rings by characterizing assembly intermediates accumulated in cells depleted of each -subunit. Starting from 2, incorporation of -subunits occurs in an orderly manner dependent on the propeptides of 2 and 5, and the C-terminal tail of 2. Unexpectedly, hUmp1, a chaperone functioning at the final assembly step, is incorporated as early as 2 and is required for the structural integrity of early assembly intermediates. We propose a model in which -ring formation is assisted by both intramolecular and extrinsic chaperones, whose roles are partially different between yeast and mammals.
Keywords:
- assembly,
- chaperone,
- propeptide,
- proteasome,
- ubiquitin
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