L. Koch, Kwaku N. Opoku, Yi Deng, Adrienne Barber, Aimee J Littleton, N. London, S. Biggins, C. Asbury
Proceedings of the National Academy of Sciences, 2019
Significance 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. Accurate mitosis depends on a surveillance system called the spindle assembly checkpoint. This checkpoint acts at kinetochores, which attach chromosomes to the dynamic tips of spindle microtubules. When a kinetochore is unattached or improperly attached, the protein kinase Mps1 phosphorylates kinetochore components, catalyzing the generation of a diffusible “wait” signal that delays anaphase and gives the cell time to correct the error. When a kinetochore becomes properly attached, its checkpoint signal is silenced to allow progression into anaphase. Recently, microtubules were found to compete directly against recombinant human Mps1 fragments for binding to the major microtubule-binding kinetochore element Ndc80c, suggesting a direct competition model for silencing the checkpoint signal at properly attached kinetochores. Here, by developing single-particle fluorescence-based assays, we tested whether such direct competition occurs in the context of native kinetochores isolated from yeast. Mps1 levels were not reduced on kinetochore particles bound laterally to the sides of microtubules or on particles tracking processively with disassembling tips. Instead, we found that Mps1 kinase activity was sufficient to promote its release from the isolated kinetochores. Mps1 autophosphorylation, rather than phosphorylation of other kinetochore components, was responsible for this dissociation. Our findings suggest that checkpoint silencing in yeast does not arise from a direct competition between Mps1 and microtubules, and that phosphoregulation of Mps1 may be a critical aspect of the silencing mechanism.
Cited by 1 publication.
Field of study: Chemistry