Fig. 1.

Chromatin dynamics at enhancers and promoters during gene activation. a Silent chromatin characterized by a regular pattern of nucleosomes positioned over regulatory elements including the enhancer and its target promoter. b Initial binding of a Pioneer TF within nucleosomes first to the enhancer facilitates the binding of additional TFs and co-factors to open the chromatin through histone modifications. c Additional TFs and the action of ATP-dependent chromatin remodeling complexes in response to hormones or other differentiation signals facilitate the recruitment of the transcription machinery to both the promoter and the enhancer. Histone variant exchange at regulatory elements may contribute to chromatin relaxation. d Physical contacts between enhancer and its target promoter occurs when the gene is transcribed. Under this condition, the enhancer is characterized by its association with high levels of the H3K27ac histone modification