The Mediator (MED) complex serves as a hub for transcriptional signaling events. MED bridges transcriptional activators and repressors. This large multi-protein complex has a central core conserved from yeast to humans. The core is composed of three modules: head, middle, and tail. A separate module, the Cdk8 kinase module, composed of Cdk8, CycC, kto and skd, serves as a regulator. (Adapted from FBrf0226415 and FBrf0191850).