About MED / Mediator Complex:
A multiprotein complex, the Mediator is one that functions in all eukaryotes as a transcriptional coactivator. It was discovered in Roger D. Kornberg’s laboratory in 1990.
Mediator complexes interact with RNA polymerase II and transcription factors. The chief function of mediator complexes is transmitting signals to the polymerase from the transcription factors.
It is possible for individual sub units to be replaced by different sub units under certain conditions. They could also be absent under specific circumstances as well.
Mediator Complex Structure
In addition to this, there are a lot of different regions within mediator proteins that are disordered intrinsically. This may end up contributing to the conformational flexibility that we see both without and with other protein complexes or bound proteins.
For the successful transcription by RNA polymerase II, mediator complex is needed. Mediator has also been proven to make contacts in the transcription preinitiation complex with the polymerase.