Ubiquitin-free routes into the proteasome.
The majority of proteasome substrates identified to date are marked for degradation by polyubiquitinylation. Exceptions to this principle, however, are well documented and can help us understand the process proteasomes use to recognize their substrates. Examples include ornithine decarboxylase, p21/Cip1, TCRalpha, IkappaBalpha, c-Jun, calmodulin and thymidylate synthase. Degradation of these proteins can be completely ubiquitin-independent or coexist with ubiquitin-dependent pathways. Uncoupling degradation from ubiquitin modification may reflect the evolutionary conservation of mechanisms optimized for highly specialized regulatory functions.
Hoyt
M A
MA
Department of Microbiology and Immunology, University of California, San Francisco, San Francisco, California 94143-0414, USA.
Coffino
P
P
D000818:Animals; D050759:Cyclin-Dependent Kinase Inhibitor p21; D016213:Cyclins / Q000378:metabolism; D003546:Cysteine Endopeptidases / Q000378:metabolism*; D006801:Humans; D009097:Multienzyme Complexes / Q000378:metabolism*; D009955:Ornithine Decarboxylase / Q000378:metabolism; D046988:Proteasome Endopeptidase Complex; D013379:Substrate Specificity; D025801:Ubiquitin / Q000378:metabolism*
C493956:CDKN1A protein, human; D050759:Cyclin-Dependent Kinase Inhibitor p21; D016213:Cyclins; D009097:Multienzyme Complexes; D025801:Ubiquitin; D003546:Cysteine Endopeptidases; D046988:Proteasome Endopeptidase Complex; D009955:Ornithine Decarboxylase