Disordered Motifs and Domains in Cell Control - October 11-15, 2014

Disordered Motifs and Domains in Cell Control

Sunday Speaker Abstracts

The Discovery and Characterisation of a Novel Class of Anaphase Promoting Complex (APC/C) Activator-binding Motif Required for Ordered Substrate Destruction and Spindle Assembly Checkpoint (SAC) Integrity Norman E. Davey 1,2,3 , Barbara Di Fiore 4,5 , Dan Lu 1,2 , Jorg Mansfeld 6 , Toby J. Gibson 3 , David O. Morgan 1,2 , Jonathan Pines 4,5 . 6 Technische Universität Dresden, Dresden, Germany. 2 University of California, San Francisco, San Francisco, CA, USA, 3 European Molecular Biology Laboratory, Heidelberg, Germany, 4 University of Cambridge, Cambridge, United Kingdom, 5 University of Cambridge, Cambridge, United Kingdom, 1 University of California, San Francisco, San Francisco, CA, USA, The APC/C ubiquitin ligase regulates mitosis by degrading specific proteins at specific times. The CDC20-like family members, CDC20 and CDH1, act as substrate recruitment subunits for the APC/C. How CDC20 and CDH1 temporally order the degradation of their substrates is a key problem in the control of cell division. Here, we have used a bioinformatics approach to identify a novel class of SLiM that mediates binding between a number of mitotic regulators and members of the CDC20-like family. We have named the motif the ABBA motif, as it is present in the A-type Cyclins, the SAC components BUBR1 and BUB1, and the CDH1 inhibitor ACM1. We demonstrate that Cyclin A, BUB1 and BUBR1 bind competitively to the same site on the APC/C co-activator CDC20. Furthermore, we show that the ABBA motif is required for Cyclin A destruction when the SAC is active. These observation provide a mechanism by which Cyclin A is degraded when the APC is inhibited by the SAC through competition with the central SAC component BUBR1. We also show that the functional homologue of Cyclin A in yeast, CLB5, contains an ABBA motif and, similarly to Cyclin A, the CLB5 ABBA motif is required for the correct ordering of protein destruction during mitotic exit in yeast. Finally, we show that the ABBA motifs in BUBR1 and BUB1 are required to recruit CDC20 to unattached kinetochores and for the SAC to work at full strength. Thus, we have identified a motif conserved through evolution that connects the recognition of APC/C substrates with the SAC, and is integral to the correct timing of protein destruction in mitosis.

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