PT  - JOURNAL ARTICLE
AU  - Chu Chen
AU  - Ian P. Whitney
AU  - Anand Banerjee
AU  - Palak Sekhri
AU  - David M. Kern
AU  - Adrienne Fontan
AU  - John J. Tyson
AU  - Iain M. Cheeseman
AU  - Ajit P. Joglekar
TI  - Ectopic activation of the Spindle Assembly Checkpoint reveals its biochemical design and physiological operation
AID  - 10.1101/154054
DP  - 2017 Jan 01
TA  - bioRxiv
PG  - 154054
4099  - http://biorxiv.org/content/early/2017/06/22/154054.short
4100  - http://biorxiv.org/content/early/2017/06/22/154054.full
AB  - Switch-like activation of the Spindle Assembly Checkpoint (SAC) is critical for accurate chromosome segregation during cell division. To determine the mechanisms that implement it, we engineered an ectopic, kinetochore-independent SAC activator, the “eSAC”. The eSAC stimulates the SAC signaling cascade by artificially dimerizing the Mps1 kinase domain and a cytosolic KNL1 phosphodomain, the signaling scaffold in the kinetochore. Quantitative analyses and mathematical modeling of the eSAC reveal that the recruitment of multiple SAC proteins by the KNL1 phosphodomain stimulates synergistic signaling, which enables a small number of KNL1 molecules produce a disproportionately strong anaphase-inhibitory signal. However, when multiple KNL1 molecules signal concurrently, they compete for a limited cellular pool of SAC proteins. This frustrates synergistic signaling and modulates signal output. Together, these mechanisms institute automatic gain control – inverse, non-linear scaling between the signal output per kinetochore and the unattached kinetochore number, and thus enact the SAC switch.