Mediator structure and rearrangements required for holoenzyme formation

Area of Science:

• Molecular Biology
• Structural Biology
• Biochemistry

Background:

• The Mediator complex is a crucial co-activator regulating RNA polymerase II transcription across eukaryotes.
• Understanding Mediator's structure and interactions is key to deciphering its role in transcription initiation and signal transduction.

Purpose of the Study:

• To elucidate the high-resolution structure of the Schizosaccharomyces pombe Mediator complex.
• To investigate the structural rearrangements of Mediator during RNA polymerase II holoenzyme formation.

Main Methods:

• Cryo-electron microscopy (cryo-EM) was used to determine the structure of Mediator at 4.4 Å resolution.
• Comparative structural analysis was performed with a Mediator-RNA polymerase II holoenzyme map (7.8 Å resolution).

Main Results:

• Individual conserved Mediator subunits were resolved within the 4.4 Å cryo-EM map.
• The Med14 subunit acts as a central scaffold, linking Mediator modules (head, middle, tail).
• Med14 structural changes were observed during holoenzyme formation, facilitating Mediator rearrangement.

Conclusions:

• The study reveals Med14's pivotal role in organizing Mediator structure and facilitating holoenzyme assembly.
• Mediator's conformational flexibility and inter-module communication are vital for integrating regulatory signals in transcription.