Diagram depicting the epigenetic landscapes present at transcriptionally repressed and active chromatin. a | Transcriptionally repressed, enzymatically inaccessible cis-regulatory elements are characterized by regularly spaced nucleosome arrays enriched for DNA methylation and specific histone modifications, such as trimethylation of lysine 27 on histone 3 (H3K27me3). b | Transcriptionally active genes exhibit enzymatically accessible cis-regulatory elements with positioned, flanking nucleosomes enriched for specific histone modifications such as acetylation. CCCTC-binding factor (CTCF) and cohesin are depicted facilitating a chromatin contact between an active enhancer and an active promoter. 5mC, 5-methylcytosine; Pol II, Polymerase II; TSS, transcription start site.