A novel mediator between activator proteins and the RNA polymerase II transcription apparatus.

Kornberg discovered that transmission of gene regulatory signals to the RNA polymerase machinery is accomplished by an additional protein complex dubbed the Mediator. As noted by the Nobel Prize committee, "the great complexity of eukaryotic organisms is actually enabled by the fine interplay between tissue-specific substances, enhancers in the DNA and Mediator. The discovery of Mediator is therefore a true milestone in the understanding of the transcription process."