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XB-ART-11884
Philos Trans R Soc Lond B Biol Sci 1999 Sep 29;3541389:1571-5; discussion 1575-6. doi: 10.1098/rstb.1999.0500.
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Mechanisms and regulation of the degradation of cyclin B.

Hershko A .


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The degradation of the cyclin B subunit of protein kinase Cdk1/cyclin B is required for inactivation of the kinase and exit from mitosis. Cyclin B is degraded by the ubiquitin pathway, a system involved in most selective protein degradation in eukaryotic cells. In this pathway, proteins are targeted for degradation by ligation to ubiquitin, a process carried out by the sequential action of three enzymes: the ubiquitin-activating enzyme E1, a ubiquitin-carrier protein E2 and a ubiquitin-protein ligase E3. In the system responsible for cyclin B degradation, the E3-like function is carried out by a large complex called cyclosome or anaphase-promoting complex (APC). In the early embryonic cell cycles, the cyclosome is inactive in the interphase, but becomes active at the end of mitosis. Activation requires phosphorylation of the cyclosome/APC by protein kinase Cdk1/cyclin B. The lag kinetics of cyclosome activation may be explained by Suc1-assisted multiple phosphorylations of partly phosphorylated complex. The presence of a Fizzy/Cdc20-like protein is necessary for maximal activity of the mitotic form of cyclosome/APC in cyclin-ubiquitin ligation.

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Species referenced: Xenopus
Genes referenced: ccnb1.2 cdc20 cdk1

References [+] :
Amon, Closing the cell cycle circle in yeast: G2 cyclin proteolysis initiated at mitosis persists until the activation of G1 cyclins in the next cycle. 1994, Pubmed