Structure of the human Mediator-bound transcription preinitiation complex

Mediating transcription The Mediator complex is recruited by transcription factors to all protein-coding genes in eukaryotes and helps to assemble the machinery necessary to transcribe the gene. Abdella et al. present the cryo–electron microscopy structure of the human Mediator-bound preinitiation complex (Med-PIC). The structure shows how Mediator positions the long, flexible C-terminal domain of RNA polymerase II to be phosphorylated by the kinase CDK7, a crucial step for further processing of the RNA into a mature RNA. Most sites where transcription factors bind to Mediator are flexibly tethered to the complex, allowing the large Med-PIC to assemble at any gene. Science , this issue p. 52