A Protocol to Purify Human Mediator Complex From Freestyle 293-F Cells

Area of Science:

• Molecular Biology
• Biochemistry
• Gene Regulation

Background:

• The Mediator complex is essential for RNA polymerase II (Pol II)-dependent transcription in eukaryotes.
• Its large size and complexity make in vitro studies challenging, particularly isolating intact human complexes.
• The CDK8 kinase module (CKM) and core Mediator (cMED) are distinct components of the Mediator.

Purpose of the Study:

• To present a novel and efficient method for purifying the intact CKM-cMED complex from human cells.
• To obtain a homogeneous Mediator complex preparation free of Pol II for further research.
• To facilitate large-scale protein purification for structural and functional analyses.

Main Methods:

• Expression of FLAG-tagged CDK8 in FreeStyle 293-F cells.
• Immunoaffinity purification from nuclear extracts.
• Glycerol gradient centrifugation for enhanced homogeneity.
• Utilizing the mutual exclusivity of CKM and Pol II binding to cMED.

Main Results:

• Successful purification of the intact CKM-cMED complex from 293-F cells.
• The isolated complex is free of RNA polymerase II (Pol II).
• The protocol is time- and cost-efficient for large-scale purification.

Conclusions:

• This protocol offers a reliable method for obtaining the endogenous Mediator complex, free of Pol II.
• The absence of crosslinkers in the purification process is advantageous for downstream structural and functional studies.
• The purified complex is suitable for detailed investigations into Mediator function and structure.