The Mediator complex: Co-transcriptional regulation and beyond

The Mediator complex functions as a central multi-subunit coactivator essential for RNA polymerase II-dependent transcription in eukaryotes, integrating signals from enhancers to promoters across the transcription cycle. This review summarizes its modular composition and structural dynamics revealed by cryo-EM, and details its mechanistic roles in pre-initiation complex assembly, promoter-proximal pausing release, elongation progression, co-transcriptional splicing, termination via 3'-end processing, and chromatin changes. Recent progress elucidates allosteric signal transmission, TF multivalency, cohesin-mediated looping, and phase separation, while dysregulation implicates Mediator in cancer and developmental disorders. Future directions emphasize in vivo kinetics, and therapeutic targeting of kinase modules to decode context-specific gene control.