Chromosomes carry our genetic material and must be precisely copied and partitioned into daughter cells during cell division. To ensure correct partitioning, a signaling cascade called the spindle assembly checkpoint delays cell division until all chromosomes are correctly attached to microtubules, the dynamic filaments that drive chromosome movements. If even a single chromosome is unattached or incorrectly attached, an enzyme, Mps1, initiates checkpoint signaling by binding to and modifying kinetochores, the large protein complexes that connect chromosomes to microtubules. Here we identify conditions that promote Mps1 release from native kinetochore particles isolated from yeast. Our findings suggest how the checkpoint “wait” signals might be turned off when kinetochores bind microtubules.
