Inter‐modular interaction between the head and CDK8 modules of Mediator regulates a recruitment of TFIIH to the promoters

Abstract

Mediator is an essential co-activator, which regulates RNA polymerase II (Pol II) transcription in eukaryotes. Mediator is a large multi-protein complex composed of four distinct sub-complexes termed Head, Middle, Tail, often termed core Mediator (cMed), as well as the CDK8 module (CKM), which is dissociable from core Mediator. While cMed regulates Pol II transcription by involving in formation and pre-initiation complex (PIC) via interaction with Pol II and general transcription factors (GTFs), the role of CKM still remains elusive. In higher eukaryotes, CKM appears to function as both in negative and positive regulator. In yeast Saccharomyces cerevisiae, CKM has been believed to function as a negative regulator. The one mode of inhibition by CKM comes from disruption of activators by triggering ubiquitin-mediated degradation by phosphorylation. However, overall the mode of transcription inhibition by CKM has not been fully understood. It is proposed that CKM inhibits transcription blocking cMed-Pol II interactions. However, genome-wide studies completely disputed this model. In this work, our structure-based functional study has led to a totally unexpected discovery that while Mediator head module facilitates recruitment of TFIIH, CKM appears to inhibit a process. In essence, the inter-modular interaction within the Mediator modules regulates conversion from initiation to elongation step of transcription by modulating a recruitment of a general transcription factor TFIIH.