Figure 4

Four representative, simplified signaling pathways are shown. Each pathway is activated by different signals; for instance, p53 signaling is activated during cell stress, toll like receptors (TLR) are activated in response to infection, and the sterol regulatory element binding protein (SREBP) is activated in response to metabolic cues. Each pathway converges on a distinct transcription factor that targets a different Mediator subunit, helping to recruit and regulate Mediator activity at select genomic loci. The end result is transcription factor-dependent activation (or repression) of a specific set of genes that are important for the response to the stimulus. Due to Mediator's role in relaying and integrating these signals directly to the transcription machinery (including the pol II enzyme itself), Mediator can be considered an endpoint of signaling cascades¹⁵².