Journal
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
Volume 97, Issue 6, Pages 2497-2502Publisher
NATL ACAD SCIENCES
DOI: 10.1073/pnas.060025497
Keywords
E3; N-end rule; ubiquitin fusion degradation pathway; Ubr1p; Ufd4p
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Funding
- NIDDK NIH HHS [R37 DK039520, DK39520, R01 DK039520, R56 DK039520] Funding Source: Medline
- NIGMS NIH HHS [GM31530, R01 GM031530] Funding Source: Medline
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The ubiquitin (Ub) system recognizes degradation signals of the target proteins through the E3 components of E3-E2 Ub ligases. A targeted substrate bears a covalently linked multi-Ub chain and is degraded by the ATP-dependent 26S proteasome, which consists of the 20S core protease and two 19S particles. The latter mediate the binding and unfolding of a substrate protein before its transfer to the interior of the 20S core. It is unclear how a targeted substrate is delivered to the 26S proteasome, inasmuch as Rpn10p, the only known proteasomal subunit that binds multi-Ub chains, has been found to he not essential for degradation of many proteins in the yeast Saccharomyces cerevisiae, Here we show that Ubr1p and Ufd4p, the E3 components of two distinct Ub ligases, directly interact with the 26S proteasome. Specifically, Ubr1p is shown to bind to the Rpn2p, Rpt1p, and Rpt6p proteins of the 19S particle, and Ufd4p is shown to bind to Rpt6p. These and related results suggest that a substrate-bound Ub ligase participates in the delivery of substrates to the proteasome, because of affinity between the ligase's E3 component and specific proteins of the 19S particle.
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