How does TFIIH facilitate the dissociation of the mediator complex?

TFIIH plays a critical role in the transcription process, particularly in the phosphorylation of the C-terminal domain (CTD) of RNA polymerase II. When TFIIH associates with RNA polymerase II, it phosphorylates serine 5 residues in the CTD. This post-translational modification is crucial because it signals the transition from transcription initiation to elongation.

The phosphorylation of serine 5 leads to the release of the mediator complex from RNA polymerase II. Essentially, when serine 5 on the CTD is phosphorylated, it promotes a conformational change in RNA polymerase II that reduces its affinity for the mediator complex, allowing the mediator to dissociate. This transition is key for the RNA polymerase to progress into the elongation phase of transcription.

While the other choices mention processes associated with transcription, they do not directly explain how TFIIH specifically influences the dissociation of the mediator complex in the context of transcription regulation. Binding to the TATA box relates to the promoter recognition phase, hydrolyzing ATP is important for the energy dynamics of transcription factors, and elongating the RNA transcript refers to a later stage of the transcription process. The action of TFIIH in phosphorylating the CTD is the