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Published February 20, 1998 | public
Journal Article

Ump1p Is Required for Proper Maturation of the 20S Proteasome and Becomes Its Substrate upon Completion of the Assembly


We report the discovery of a short-lived chaperone that is required for the correct maturation of the eukaryotic 20S proteasome and is destroyed at a specific stage of the assembly process. The S. cerevisiae Ump1p protein is a component of proteasome precursor complexes containing unprocessed β subunits but is not detected in the mature 20S proteasome. Upon the association of two precursor complexes, Ump1p is encased and is rapidly degraded after the proteolytic sites in the interior of the nascent proteasome are activated. Cells lacking Ump1p exhibit a lack of coordination between the processing of β subunits and proteasome assembly, resulting in functionally impaired proteasomes. We also show that the propeptide of the Pre2p/Doa3p β subunit is required for Ump1p's function in proteasome maturation.

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© 1998 Cell Press. Under an Elsevier user license. Received 10 December 1997, Revised 16 January 1998. We thank Rohan Baker, Anthony Bretscher, Ricardo Ferreira, Wolfgang Heinemeyer, Wolfgang Hilt, Mark Hochstrasser, Carl Mann, Nancy Kleckner, Keiji Tanaka, and Dieter Wolf for the gifts of plasmids, yeast strains, and antisera; Elisabeth Andrews for assistance in the cloning of UMP1, Reiner Stappen for assistance in producing anti-Ump1p antibodies, Robert Kramer (Limberg Druck) for printing the figures, and Nils Johnsson and Ralf Kölling for helpful suggestions. P. C. R., J. H., and R. J. D. are grateful to Cornelis P. Hollenberg for providing lab space and for his support, and to Isabel Fuchs for technical assistance. P. C. R. was supported by a postdoctoral fellowship from Fundação para a Ciência e Tecnologia, Programa Praxis XXI. This work was supported by a grant to R. J. D. from the Bundesministerium für Bildung, Wissenschaft, Forschung und Technologie (0316711), by start-up funding from the Ministerium für Wissenschaft und Bildung des Landes Nordrhein-Westfalen, and by a grant to A. V. from the National Institutes of Health (GM31530).

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