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. Author manuscript; available in PMC: 2014 Mar 7.
Published in final edited form as: Mol Cell. 2013 Mar 7;49(5):10.1016/j.molcel.2013.01.038. doi: 10.1016/j.molcel.2013.01.038

Figure 1.

Figure 1

Epigenetic features of active, primed and poised enhancers. (A) Schematic representation of the major chromatin features found at active enhancers. Enhancers are associated with incorporation of hypermobile nucleosomes containing H3.3/H2A.Z histone variants, which compete for DNA binding with TFs. TFs in turn recruit coactivator proteins that can modify and remodel nucleosomes. H3K4me1 and H3K27ac are the predominant histone modifications deposited at nucleosomes flanking enhancer elements. (B) Prior to activation, enhancers can exist in a primed state, characterized by the presence of H3K4me1. Other features that have been associated with enhancer priming are presence of pioneer TFs, hypermobile H3.3/H2A.Z nucleosomes, DNA 5mC hypomethylation and hydroxylation (5hmC). (C) Schematic representation of the chromatin landscape surrounding poised enhancers found in human and mouse ESC. A subset of “primed” enhancers in ESC is also marked by H3K27me3 and associated with PRC2. These enhancers are bound by TFs and coactivators and communicate with their target promoters.