Endogenous mediators are intracellular proteins that enhance and activate the functions of other proteins. This term is commonly used in molecular biology and cell biology to describe a specific protein complex that acts in transcription as a coactivator. This Mediator complex is located within the cell nucleus.
The Mediator complex is required for the successful transcription of nearly all class II gene promoters in yeast.[1] It works in the same manner in mammals. The mediator functions as a coactivator and binds to the C-terminal domain of RNA polymerase II holoenzyme, acting as a bridge between this enzyme and transcription factors.[2]