Coordination of transcription, processing, and export of highly expressed RNAs by distinct biomolecular condensates.

Abstract

Genes under control of super-enhancers are expressed at extremely high levels and are frequently associated with nuclear speckles. Recent data suggest that the high concentration of unphosphorylated RNA polymerase II (Pol II) and Mediator recruited to super-enhancers create phase-separated condensates. Transcription initiates within or at the surface of these phase-separated droplets and the phosphorylation of Pol II, associated with transcription initiation and elongation, dissociates Pol II from these domains leading to engagement with nuclear speckles, which are enriched with RNA processing factors. The transitioning of Pol II from transcription initiation domains to RNA processing domains effectively co-ordinates transcription and processing of highly expressed RNAs which are then rapidly exported into the cytoplasm.