Structures of transcription pre-initiation complex with TFIIH and Mediator

Area of Science:

• Molecular Biology
• Structural Biology
• Biochemistry

Background:

• RNA polymerase II (Pol II) initiates transcription by forming a pre-initiation complex (PIC) with general transcription factors on promoter DNA.
• Understanding the structural basis of PIC assembly and function is crucial for deciphering gene regulation.

Purpose of the Study:

• To determine the high-resolution cryo-electron microscopy (cryo-EM) structures of the Saccharomyces cerevisiae PIC and PIC-core Mediator complex.
• To elucidate the roles of transcription factor IIH (TFIIH) core and kinase modules in promoter DNA opening and Pol II phosphorylation.

Main Methods:

• Cryo-electron microscopy (cryo-EM) was used to obtain structures of the PIC and PIC-core Mediator complex.
• Nominal resolutions of 4.7 Å and 5.8 Å were achieved for the PIC and PIC-core Mediator complex, respectively.

Main Results:

• The structures reveal the precise positioning of TFIIH subunits, including Ssl2, within the PIC, consistent with TFIIE-stimulated DNA opening.
• The TFIIH kinase module subunit Tfb3 anchors the kinase Kin28 (CDK7), which is mobile but preferentially located near the Mediator complex.
• Identified open spaces within the Mediator complex suggest potential access routes for Kin28 to phosphorylate the C-terminal domain of Pol II.

Conclusions:

• The study provides unprecedented structural insights into the Saccharomyces cerevisiae PIC and its core Mediator complex.
• The findings clarify the functional roles of TFIIH modules in promoter DNA unwinding and Pol II C-terminal domain phosphorylation.
• This work advances our understanding of the intricate mechanisms governing the initiation of eukaryotic transcription.