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Fig. 3 | Genome Biology

Fig. 3

From: Mechanisms of enhancer action: the known and the unknown

Fig. 3

A schematic for transcriptional coordination between the enhancer, promoter, and gene body. a Multiple protein complexes specializing in many structural and catalytic activities establish EPC. RNAPII recruitment and transcription initiation occur in a phase-separated condensate (a “transcription bubble”) where productive transcript elongation takes place. RNAPII remains within the EPC-encompassing transcription bubble, necessitating extrusion of the downstream template DNA into a loop behind—as elongation proceeds. Sequential recruitment of RNAPII represent transcription of the gene in multiple transcription units, each forming a DNA loop as in the petals of a sunflower. b Additionally, the chromatin landscape of a transcriptionally poised gene can exist in a sunflower arrangement where proteins assembled at intronic TFBS clusters hold the enhancer and promoter in proximity without direct EPC. Transcription initiation accompanies direct EPC. This model can supplement and co-operate with (a). c Multiple gene promoters can exist in physical proximity with a given enhancer within a phase-separated condensate, facilitating coordinated transcription activation. Likewise, a given promoter can also exist in association with multiple enhancers simultaneously

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