Figure 1.

Simplified scheme of condensed heterochromatin and open chromatin features. Heterochromatin is mostly hypo-acetylated, marked by methylated lysine 9 on histone H3 (H3K9me2/3) which forms a binding site for heterochromatin protein 1 (HP1), contains methylated DNA, and results from the action of repressive complexes such as histone deacetylases (HDACs), H3K9 methyltransferases (H3K9-MT), and DNA methyltransferases (Dnmts). Chromatin opening is orchestrated by the concerted action of transcription factors (TFs) and chromatin modifying enzymes such as histone methyltransferases (HMTs), histone acetyl transferases (HATs), and SWI/SNF remodeling complexes. Open chromatin is generally acetylated, harbors active histone marks, and is accessible to the transcription machinery and RNA polymerase II (Pol II). TF binding sites (TFBSs) are indicated by yellow rectangles and the nucleosomes consisting of histone octamers are depicted by green cylinders. For simplicity, only a single histone tail is shown protruding out of each nucleosome and DNA methylation is not depicted.