The spindle assembly checkpoint (SAC) keeps the APC/C ubiquitin ligase inactive until all chromosomes are attached to the spindle. Pines and colleagues tagged endogenous cyclin A with a fluorescent protein by gene targeting and used cyclin A degradation as an assay for SAC activity. They found that the SAC does not show an all-or-nothing response—instead, SAC strength depends on the amount of MAD2 (a checkpoint protein) at kinetochores.
- Philippe Collin
- Oxana Nashchekina
- Jonathon Pines
