Control and enzymatic activation of the APC/C ubiquitin ligase system

CDK1 and APC/C are two key regulatory enzymes controlling the cell division, growth, differentiation and death, through phosphorylation and ubiquitylation, respectively. Although it has long been apparent that phosphorylation modifies APC/C function, the challenges posed by the need for functional assays to study this control puts the elucidation of the molecular basis of phosphorylation control beyond our grasp. We have recently overcome these limitations with a pipeline that uses reconstituted recombinant APC/C in Xenopus cell free extracts to show how CDK1 activates the APC/C through coordinated phosphorylation of Apc3 and Apc1. We will now extend this pipeline with targeted assays that will determine how phosphatases regulate these phosphorylation events. Because we have found that the disordered loop domains of APC/C subunits are targets for both post-translational modifications (PTMs) and interacting partners, including protein phosphatases, we will study how the loop domain controls the APC/C. Cell cycle specific and stress-dependent PTMs and binding proteins will be identified and we will determine their impact upon APC/C-dependent ubiquitylation. This approach of combining high throughput reconstitution mutated apo-APC/C in extracts from which any component of interest can be depleted offers a unique opportunity to gain an unprecedented insight into APC/C function and control.