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. Author manuscript; available in PMC: 2019 Dec 1.
Published in final edited form as: Nat Rev Genet. 2018 Dec;19(12):789–800. doi: 10.1038/s41576-018-0060-8

Figure 4. CTCF loops and enhancer-promoter interactions.

Figure 4.

A. CTCF loops establish domains in which sequences can interact more frequently. These contacts are thought to help promote enhancer (yellow with orange transcription factor) – promoter (pink with purple RNAPII) (E-P) interactions when inside the domain, but help insulate against those outside the domain. However, examples of genes that escape the CTCF domain and interact with adjacent sequences can be observed in Hi-C data (arrow). It is likely that these “escapee” genes interact with promoters or regulatory sequences within A compartmental domains (large light pink oval).

B. A speculative model of transcriptional activation. In this model, genes are inactive when extrusion has not begun (top) and are activated once extrusion brings together enhancers and promoters (left). Gene activity is lost once extrusion moves past the enhancer or promoter (right), but will be reestablished during each extrusion event. Regular extrusion events causing gene activation at discrete times may explain transcriptional bursting.