Editing Histone fold (section)

== Structure ==

The histone fold is typically around 70 [[amino acids]] long and is characterized by three [[alpha helices]] connected by two short, unstructured loops.<ref name = "Alva_2007">{{cite journal | vauthors = Alva V, Ammelburg M, Söding J, Lupas AN | title = On the origin of the histone fold | journal = BMC Structural Biology | volume = 7 | issue = 1 | pages = 17 | date = March 2007 | pmid = 17391511 | pmc = 1847821 | doi = 10.1186/1472-6807-7-17 | doi-access = free }}</ref> In the absence of DNA, core histones assemble into head-to-tail intermediates. For instance, [[Histone H3|H3]] and [[Histone H4|H4]] first form heterodimers, which then combine to form a tetramer. Similarly, [[Histone H2A|H2A]] and [[Histone H2B|H2B]] form heterodimers.<ref>{{cite book | vauthors = Watson JD, Baker TA, Bell SP, Gann A, Levine MK, Losick R |title=Molecular Biology of the Gene |date=2008 |publisher=Pearson/Benjamin Cummings |isbn=978-0-8053-9592-1 }}{{page needed|date=July 2020}}</ref> These interactions occur through hydrophobic "handshake" interactions between histone fold domains.<ref name=pmid7479959>{{cite journal | vauthors = Arents G, Moudrianakis EN | title = The histone fold: a ubiquitous architectural motif utilized in DNA compaction and protein dimerization | journal = Proceedings of the National Academy of Sciences of the United States of America | volume = 92 | issue = 24 | pages = 11170–11174 | date = November 1995 | pmid = 7479959 | pmc = 40593 | doi = 10.1073/pnas.92.24.11170 | doi-access = free | bibcode = 1995PNAS...9211170A }}</ref> 

Histones H4 and H2A can form internucleosomal contacts that, when [[acetylated]], enable ionic interactions between peptides. These interactions can alter the surrounding internucleosomal contacts, leading to chromatin opening and increased accessibility for transcription.<ref>{{cite journal | vauthors = Mariño-Ramírez L, Kann MG, Shoemaker BA, Landsman D | title = Histone structure and nucleosome stability | journal = Expert Review of Proteomics | volume = 2 | issue = 5 | pages = 719–729 | date = October 2005 | pmid = 16209651 | pmc = 1831843 | doi = 10.1586/14789450.2.5.719 }}</ref>