The structural and functional organization of the yeast mediator complex

Area of Science:

• Molecular Biology
• Gene Regulation
• Biochemistry

Background:

• The Mediator complex is crucial for RNA polymerase II (pol II) transcription in Saccharomyces cerevisiae.
• Mediator comprises two main subcomplexes: Rgr1 and Srb4, each with distinct roles.
• Understanding the structural and functional organization of Mediator subcomplexes is key to deciphering transcription regulation.

Purpose of the Study:

• To elucidate the structures and functions of the Rgr1 and Srb4 subcomplexes of yeast Mediator.
• To investigate the interactions of Mediator subcomplexes with each other and with basal transcription machinery.
• To determine how Mediator's modular organization contributes to transcription regulation.

Main Methods:

• Expression and purification of recombinant Mediator subunits.
• Assays for protein-protein interactions within Mediator subcomplexes.
• Analysis of Mediator subcomplex interactions with basal transcription factors and pol II.

Main Results:

• The Rgr1 subcomplex includes the Gal11 (activator-binding) and Med9/10 modules, with Med9 interacting with Srb10/11, suggesting a role in repression.
• The Srb4 subcomplex stimulates basal pol II transcription but has minimal impact on activated transcription or Rpb1 C-terminal domain phosphorylation.
• Both Rgr1 and Srb4 subcomplexes interact with distinct sets of basal transcription factors and pol II.

Conclusions:

• Mediator's modular structure allows for distinct functional roles of its subcomplexes in transcription.
• The Rgr1 subcomplex mediates both activation and repression, potentially through its distinct modules.
• Mediator likely recruits and stabilizes the preinitiation complex via multiple interactions with regulators and basal factors.