Epigenetic chromatin regulation. Top, silenced chromatin inaccessible to transcription factors and some of its typical epigenetic modifications; Bottom, active chromatin accessible to transcription factors with some of its typical epigenetic modifications. Selected chromatin modifiers regulating the transitions between the two are presented at the sides of the arrows. Blue, DNA; orange, core nucleosome; green, linker histone H1 (darker shade for the least dynamic, lighter shade for the most dynamic); black oval, heterochromatin protein 1; gray oval, transcription factor TF; Gray rectangle, high mobility group proteins; dash arrows, disassembly and reassembly. Me/2/3, methylation, di- or tri-; Ac, acetylation; P, phosphorylation.