Illustration of epigenetic modifications on histones and DNA

The genome is compacted by wrapping a 147 base-pair strand of DNA around a core of eight histone proteins to create nucleosomes, which are then further compacted into chromatin and chromosomes (top panel). A subset of covalent modifications (yellow circles) on both the histone and DNA components control accessibility of DNA to transcription factors and other regulators, and form the basis of epigenetic modifications. These epigenetic marks are established by "writers," such as KMTs, HATs, and DNMTs. They are interpreted by "readers," including MBD proteins on the DNA and multiple proteins for the histone marks as shown. Almost all of the marks can be removed by "erasers," such as KDMs, HDACs, and by the TET family of 5‑methylcytosine oxidases. The interplay between these enzymes helps to establish and maintain cellular identity by regulating access to the DNA sequence, along with the central role of transcription factors.