Signaling protein abundance modulates the strength of the spindle assembly checkpoint.

During mitosis, unattached kinetochores in a dividing cell signal to the spindle assembly checkpoint (SAC) to delay anaphase onset and prevent chromosome missegregation. The signaling activity of these kinetochores and the likelihood of chromosome missegregation depend on the amount of SAC signaling proteins each kinetochore recruits. Therefore, factors that control SAC protein recruitment must be thoroughly understood.