The mitotic checkpoint complex binds a second CDC20 to inhibit active APC/C.
The spindle assembly checkpoint (SAC) maintains genomic stability by delaying chromosome segregation until the last chromosome has attached to the mitotic spindle. The SAC prevents the anaphase promoting complex/cyclosome (APC/C) ubiquitin ligase from recognizing cyclin B and securin by catalysing the incorporation of the APC/C co-activator, CDC20, into a complex called the mitotic checkpoint complex (MCC). The SAC works through unattached kinetochores generating a diffusible 'wait anaphase' signal that inhibits the APC/C in the cytoplasm, but the nature of this signal remains a key unsolved problem. Moreover, the SAC and the APC/C are highly responsive to each other: the APC/C quickly targets cyclin B and securin once all the chromosomes attach in metaphase, but is rapidly inhibited should kinetochore attachment be perturbed. How this is achieved is also unknown. Here, we show that the MCC can inhibit a second CDC20 that has already bound and activated the APC/C. We show how the MCC inhibits active APC/C and that this is essential for the SAC. Moreover, this mechanism can prevent anaphase in the absence of kinetochore signalling. Thus, we propose that the diffusible 'wait anaphase' signal could be the MCC itself, and explain how reactivating the SAC can rapidly inhibit active APC/C.
The Gurdon Institute and Department of Zoology, Tennis Court Road, Cambridge CB2 1QN, UK.
Daisuke
D
Izawa
The Gurdon Institute and Department of Zoology, Tennis Court Road, Cambridge CB2 1QN, UK.
Jonathon
J
Pines
D000705:Anaphase; D064173:Anaphase-Promoting Complex-Cyclosome / Q000037:antagonists & inhibitors* / Q000378:metabolism; D000818:Animals; D064199:Cdc20 Proteins / Q000378:metabolism*; D003593:Cytoplasm / Q000201:enzymology / Q000378:metabolism; D006367:HeLa Cells; D006801:Humans; D059566:M Phase Cell Cycle Checkpoints; D008938:Mitosis; D046912:Multiprotein Complexes / Q000378:metabolism*; D011485:Protein Binding; D017346:Protein Serine-Threonine Kinases / Q000737:chemistry / Q000378:metabolism; D017434:Protein Structure, Tertiary; D008941:Spindle Apparatus / Q000378:metabolism; D013379:Substrate Specificity
D064199:Cdc20 Proteins; D046912:Multiprotein Complexes; D064173:Anaphase-Promoting Complex-Cyclosome; C584277:BUB1 protein, human; D017346:Protein Serine-Threonine Kinases