The APC/C maintains the spindle assembly checkpoint by targeting Cdc20 for destruction.
The spindle assembly checkpoint (SAC) is required to block sister chromatid separation until all chromosomes are properly attached to the mitotic apparatus. The SAC prevents cells from entering anaphase by inhibiting the ubiquitylation of cyclin B1 and securin by the anaphase promoting complex/cyclosome (APC/C) ubiquitin ligase. The target of the SAC is the essential APC/C activator Cdc20. It is unclear how the SAC inactivates Cdc20 but most current models suggest that Cdc20 forms a stable complex with the Mad2 checkpoint protein. Here we show that most Cdc20 is not in a complex with Mad2; instead Mad2 is required for Cdc20 to form a complex with another checkpoint protein, BubR1. We further show that during the SAC, the APC/C ubiquitylates Cdc20 to target it for degradation. Thus, ubiquitylation of human Cdc20 is not required to release it from the checkpoint complex, but to degrade it to maintain mitotic arrest.
Nilsson
Jakob
J
Wellcome/CR UK Gurdon Institute and Department of Zoology, Tennis Court Road, Cambridge CB2 1QN, UK.
Yekezare
Mona
M
Minshull
Jeremy
J
Pines
Jonathon
J
D020816:Amino Acid Motifs; D064173:Anaphase-Promoting Complex-Cyclosome; D002135:Calcium-Binding Proteins / Q000378:metabolism; D064199:Cdc20 Proteins; D018797:Cell Cycle Proteins / Q000737:chemistry / Q000378:metabolism*; D002850:Chromatography, Gel; D006367:HeLa Cells; D006801:Humans; D008239:Lysine / Q000378:metabolism; D064246:Mad2 Proteins; D050505:Mutant Proteins / Q000378:metabolism; D011485:Protein Binding; D011499:Protein Processing, Post-Translational; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D012097:Repressor Proteins / Q000378:metabolism; D008941:Spindle Apparatus / Q000378:metabolism*; D043743:Ubiquitin-Protein Ligase Complexes / Q000378:metabolism*; D054875:Ubiquitination
D002135:Calcium-Binding Proteins; D064199:Cdc20 Proteins; D018797:Cell Cycle Proteins; C577697:MAD2L1 protein, human; D064246:Mad2 Proteins; D050505:Mutant Proteins; D012097:Repressor Proteins; C577488:CDC20 protein, human; D043743:Ubiquitin-Protein Ligase Complexes; D064173:Anaphase-Promoting Complex-Cyclosome; C584277:BUB1 protein, human; C090464:Bub1 spindle checkpoint protein; D017346:Protein Serine-Threonine Kinases; D008239:Lysine