A complex molecular switch directs stress-induced cyclin C nuclear release through SCF-mediated degradation of Med13.

In response to oxidative stress, cells decide whether to mount a survival or cell death response. The conserved cyclin C and its kinase partner Cdk8 play a key role in this decision. Both are members of the Cdk8 kinase module, which, with Med12 and Med13, associate with the core mediator complex of RNA polymerase II. In , oxidative stress triggers Med13 destruction, which thereafter releases cyclin C into the cytoplasm. Cytoplasmic cyclin C associates with mitochondria, where it induces hyperfragmentation and regulated cell death. In this report, we show that residues 742-844 of Med13's 600-amino acid intrinsic disordered region (IDR) both directs cyclin C-Cdk8 association and serves as the degron that mediates ubiquitin ligase SCF-dependent destruction of Med13 following oxidative stress. Here, cyclin C-Cdk8 phosphorylation of Med13 most likely primes the phosphodegron for destruction. Next, pro-oxidant stimulation of the cell wall integrity pathway MAP kinase Slt2 initially phosphorylates cyclin C to trigger its release from Med13. Thereafter, Med13 itself is modified by Slt2 to stimulate SCF-mediated destruction. Taken together, these results support a model in which this IDR of Med13 plays a key role in controlling a molecular switch that dictates cell fate following exposure to adverse environments.