What is the role of the mediator complex in gene transcription?

The mediator complex plays a critical role in the regulation of gene transcription by acting as a bridge between gene-specific transcription factors and the general transcription machinery. It does not directly bind to DNA sequences nor does it synthesize RNA itself. Instead, its primary function is to facilitate the assembly of the transcriptional machinery at the promoter, thereby effectively connecting different regulatory elements.

When considering the function that involves the melting of DNA, it is important to highlight that the mediator complex interacts with the carboxyl-terminal domain (CTD) of RNA polymerase II, which is a crucial component involved in the initiation of transcription. During this process, the mediator is involved in recruiting the general transcription factors, including TFIIH, that are necessary for the formation of the transcription pre-initiation complex. TFIIH has helicase activity that unwinds the DNA, allowing the RNA polymerase to access the template strand effectively.

Thus, the mediator complex is instrumental in coordinating these events, ensuring that the transcription machinery is correctly positioned and activated at the promoter region to initiate RNA synthesis.