Disrupting mediator with a short peptide ligand.

Although RNA polymerase II is the core enzyme that carries out transcription, it requires a large number of accessory proteins and protein complexes to regulate its activity. One of the most important of these complexes is Mediator, a group of 20–25 protein components that is highly conserved from Saccharomyces cerevisiae through to humans. The yeast Mediator is subdivided into three portions: a head region that contacts RNA polymerase II, a middle region, and a tail (Figure 1).