Editing Euchromatin (section)

== Regulation ==
Euchromatin is primarily regulated by [[post-translational modification]]s to its nucleosomes' [[histone]]s, conducted by many [[histone-modifying enzymes]]. These modifications occur on the histones' [[N-terminus|N-terminal]] tails that protrude from the nucleosome structure, and are thought of to recruit enzymes to either keep the chromatin in its open form, as euchromatin, or in its closed form, as [[heterochromatin]].<ref name="Bannister_2011">{{cite journal | vauthors = Bannister AJ, Kouzarides T | title = Regulation of chromatin by histone modifications | journal = Cell Research | volume = 21 | issue = 3 | pages = 381–395 | date = March 2011 | pmid = 21321607 | doi = 10.1038/cr.2011.22 | pmc = 3193420 }}</ref> [[Histone acetylation and deacetylation|Histone acetylation]], for instance, is typically associated with euchromatin structure, whereas [[histone methylation]] promotes heterochromatin remodeling.<ref name="Singh_2020">{{cite book | vauthors = Singh D, Nishi K, Khambata K, Balasinor NH | chapter = Introduction to epigenetics: basic concepts and advancements in the field|date= January 2020 | title = Epigenetics and Reproductive Health|volume=21|pages=xxv–xliv| veditors = Tollefsbol T |series=Translational Epigenetics|publisher=Academic Press|language=en| doi = 10.1016/B978-0-12-819753-0.02001-8 | isbn = 978-0-12-819753-0| s2cid = 235031860}}</ref> Acetylation makes the histone group more negatively charged, which in turn disrupts its interactions with the DNA strand, essentially "opening" the strand for easier access.<ref name="Bannister_2011" /> Acetylation can occur on multiple [[lysine]] residues of a histone's [[N-terminus|N-terminal]] tail and in different histones of the same nucleosome, which is thought to further increase DNA accessibility for [[transcription factor]]s.<ref name="Bannister_2011" />

[[Phosphorylation]] of histones is another method by which euchromatin is regulated.<ref name="Bannister_2011" /> This tends to occur on the N-terminal tails of the histones, however some sites are present in the core.<ref name="Bannister_2011" /> Phosphorylation is controlled by [[kinases]] and [[phosphatase]]s, which add and remove the phosphate groups respectively. This can occur at [[serine]], [[threonine]], or [[tyrosine]] residues present in euchromatin.<ref name="Bannister_2011" /><ref name="Singh_2020" /> Since the phosphate groups added to the structure will incorporate a negative charge, it will promote the more relaxed "open" form, similar to acetylation.<ref name="Singh_2020" /> In regards to functionality, histone phosphorylation is involved with gene expression, DNA damage repair, and [[chromatin remodeling]].<ref name="Singh_2020" />

Another method of regulation that incorporates a negative charge, thereby favoring the "open" form, is [[ADP-ribosylation|ADP ribosylation]].<ref name="Singh_2020" /> This process adds one or more [[Adenosine diphosphate ribose|ADP-ribose]] units to the histone, and is involved in the [[DNA-damage response|DNA damage response]] pathway.<ref name="Singh_2020" />