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Query: EC:6.3.2.19 (ubiquitin-protein ligase)
 799 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Cyclin B is degraded at the onset of anaphase by a ubiquitin-dependent proteolytic system. We have fractionated mitotic Xenopus egg extracts to identify components required for this process. We find that UBC4 and at least one other ubiquitin-conjugating enzyme can support cyclin B ubiquitination. The mitotic specificity of cyclin ubiquitination is determined by a 20S complex that contains homologs of budding yeast CDC16 and CDC27. Because these proteins are required for anaphase in yeast and mammalian cells, we refer to this complex as the anaphase-promoting complex (APC). CDC27 antibodies deplete APC activity, while immunopurified CDC27 complexes are sufficient to complement either interphase extracts or a mixture of recombinant UBC4 and the ubiquitin-activating enzyme E1. These results suggest that APC functions as a regulated ubiquitin-protein ligase that targets cyclin B for destruction in mitosis.
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PMID:A 20S complex containing CDC27 and CDC16 catalyzes the mitosis-specific conjugation of ubiquitin to cyclin B. 773 80

The abundance of B-type cyclin-CDK complexes is determined by regulated synthesis and degradation of cyclin subunits. Cyclin proteolysis is required for the final exit from mitosis and for the initiation of a new cell cycle. In extracts from frog or clam eggs, degradation is accompanied by ubiquitination of cyclin. Three genes, CDC16, CDC23, and CSE1 have recently been shown to be required specifically for cyclin B proteolysis in yeast. To test whether these genes are required for cyclin ubiquitination, we prepared extracts from G1-arrested yeast cells capable of conjugating ubiquitin to the B-type cyclin Clb2. The ubiquitination activity was cell cycle regulated, required Clb2's destruction box, and was low if not absent in cdc16, cdc23, cdc27, and cse1 mutants. Furthermore all these mutants were also defective in ubiquitination of another mitotic B-type cyclin, Clb3. The Cdc16, Cdc23, and Cdc27 proteins all contain several copies of the tetratricopeptide repeat and are subunits of a complex that is required for the onset of anaphase. The finding that gene products that are required for ubiquitination of Clb2 and Clb3 are also required for cyclin proteolysis in vivo provides the best evidence so far that cyclin B is degraded via the ubiquitin pathway in living cells. Xenopus homologues of Cdc16 and Cdc27 have meanwhile been shown to be associated with a 20S particle that appears to function as a cell cycle-regulated ubiquitin-protein ligase.
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PMID:TPR proteins required for anaphase progression mediate ubiquitination of mitotic B-type cyclins in yeast. 874 51

Ubiquitin-mediated proteolysis of cell cycle regulators is a major element of the cell cycle control. The anaphase-promoting complex (APC/C) is a large multisubunit ubiquitin-protein ligase required for the ubiquitination and degradation of G1 and mitotic checkpoint regulators. APC/C-dependent proteolysis regulates cyclin levels in G1, and triggers the separation of sister chromatids at the metaphase-anaphase transition and the destruction of mitotic cyclins at the end of mitosis. Furthermore, it was recently shown that APC/C regulates the degradation of crucial regulators of signal transduction pathways. We report here gene alterations in several components of this complex in human colon cancer cells, including APC6/CDC16 and APC8/CDC23 which are known to be key function elements. The experimental expression of a truncation mutant of APC8/CDC23 subunit (CDC23DeltaTPR) leads to abnormal levels of APC/C targets such as cyclin B1 and disturbs the cell cycle progression of colon epithelial cells through mitosis. Overall, these data support the hypothesis of a deleterious role of these mutations during colorectal carcinogenesis.
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PMID:Alterations of anaphase-promoting complex genes in human colon cancer cells. 1262 11