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11. BubR1 recruitment to the kinetochore via Bub1 enhances spindle assembly checkpoint signaling

Author

Banerjee, Anand, Chen, Chu, Humphrey, Lauren, Tyson, John J., Joglekar, Ajit P., Banerjee, Anand, Chen, Chu, Humphrey, Lauren, Tyson, John J., and Joglekar, Ajit P.

Abstract

During mitosis, unattached kinetochores in a dividing cell activate the spindle assembly checkpoint (SAC) and delay anaphase onset by generating the anaphase-inhibitory mitotic checkpoint complex (MCC). These kinetochores generate the MCC by recruiting its constituent proteins, including BubR1. In principle, BubR1 recruitment to signaling kinetochores should increase its local concentration and promote MCC formation. However, in human cells BubR1 is mainly thought to sensitize the SAC to silencing. Whether BubR1 localization to signaling kinetochores by itself enhances SAC signaling remains unknown. Therefore, we used ectopic SAC activation (eSAC) systems to isolate two molecules that recruit BubR1 to the kinetochore, the checkpoint protein Bub1 and the KI and MELT motifs in the kinetochore protein KNL1, and observed their contribution to eSAC signaling. Our quantitative analyses and mathematical modeling show that Bub1-mediated BubR1 recruitment to the human kinetochore promotes SAC signaling and highlight BubR1’s dual role of strengthening the SAC directly and silencing it indirectly.

Published
2022

26. Supplementary Material from Kre28-Spc105 interaction is essential for Spc105 loading at the kinetochore

Author

Roy, Babhrubahan, Sim, Janice, Han, Simon J. Y., and Joglekar, Ajit P.

Abstract

Kinetochore (KTs) are macromolecular protein assemblies that attach sister chromatids to spindle microtubules (MTs) and mediate accurate chromosome segregation during mitosis. The outer KT consists of the KMN network, a protein super-complex comprising Knl1 (yeast Spc105), Mis12 (yeast Mtw1), and Ndc80 (yeast Ndc80), which harbours sites for MT binding. Within the KMN network, Spc105 acts as an interaction hub of components involved in spindle assembly checkpoint (SAC) signalling. It is known that Spc105 forms a complex with KT component Kre28. However, where Kre28 physically localizes in the budding yeast KT is not clear. The exact function of Kre28 at the KT is also unknown. Here, we investigate how Spc105 and Kre28 interact and how they are organized within bioriented yeast KTs using genetics and cell biological experiments. Our microscopy data show that Spc105 and Kre28 localize at the KT with a 1 : 1 stoichiometry. We also show that the Kre28-Spc105 interaction is important for Spc105 protein turn-over and essential for their mutual recruitment at the KTs. We created several truncation mutants of kre28 that affect Spc105 loading at the KTs. When over-expressed, these mutants sustain the cell viability, but SAC signalling and KT biorientation are impaired. Therefore, we conclude that Kre28 contributes to chromosome biorientation and high-fidelity segregation at least indirectly by regulating Spc105 localization at the KTs.

Published
2021
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37. Ectopic Activation of the Spindle Assembly Checkpoint Signaling Cascade Reveals Its Biochemical Design

Author

Hubrecht Institute with UMC, CMM Sectie Molecular Cancer Research, Chen, Chu, Whitney, Ian P., Banerjee, Anand, Sacristan, Carlos, Sekhri, Palak, Kern, David M., Fontan, Adrienne, Kops, Geert J.P.L., Tyson, John J., Cheeseman, Iain M., Joglekar, Ajit P., Hubrecht Institute with UMC, CMM Sectie Molecular Cancer Research, Chen, Chu, Whitney, Ian P., Banerjee, Anand, Sacristan, Carlos, Sekhri, Palak, Kern, David M., Fontan, Adrienne, Kops, Geert J.P.L., Tyson, John J., Cheeseman, Iain M., and Joglekar, Ajit P.

Published
2019

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