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.
Pubmed ID: 18997788 RIS Download
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Digital microscopy software for research microscopy. It comes standard with drivers to control numerous instruments in and around the microscope. When online, data is acquired in a native-3D format over time, color and specimen locations in customizable experiment protocols. Data can be analyzed by a wide variety of tools for image processing including mathematical operations, statistics functions, analysis scripting and import to/export from MATLAB. Additional modules are available for special applications ranging from deconvolution to photomanipulation to multiphoton.
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