Histone code 5462098 215737784 2008-05-29T14:09:35Z DOI bot 6652755 Citation maintenance. Initiated by [[User:tarun2k|tarun2k]]. You can [[WP:DOI|use this bot]] yourself! Please [[User:DOI_bot/bugs|report any bugs]]. The '''Histone Code''' is hypothesized to be a code consisting of covalent [[histone]] tail modifications. Together with other modifications as [[DNA methylation]] it is part of the [[epigenetic code]]. The main role of histones is in associating with [[DNA]] to form [[nucleosome]]s, which themselves bundle to form [[chromatin]] fibers. They are globular proteins with a flexible [[N-terminus]] (taken to be the tail) that protrudes from the nucleosome. The chromatin structure plays an important role in regulation of gene expression, while the tail modifications play an important role in the chromatin structure. For details of gene expression regulation by histone modifications see [[Histone#Influence_on_gene_expression_in_mammalian_cells:|table]]. ==The Hypothesis== The hypothesis is that [[chromatin]]-DNA interactions are guided by combinations of histone modifications. While it is accepted that modulations (such as [[methylation]], [[acetylation]], ADP-ribosylation, [[ubiquitination]] and [[phosphorylation]]) to [[histone]] tails alter chromatin structure, a complete understanding of the precise mechanisms by which these alterations to histone tails influence DNA-histone interactions remains elusive. However, some specific examples have been worked out in detail. For example, phosphorylation of [[serine]] residues 10 and 28 on [[histone H3]] is a marker for chromosomal condensation. Similarly, the combination of phosphorylation of [[serine]] residue 10 and acetylation of a [[lysine]] residue 14 on histone H3 is a tell-tale sign of active [[Transcription (genetics)|transcription]]. ===Modifications=== Possible modifications to the tails are: *[[Acetylation]] - by [[HAT]] (Histone Acetyl Transferase); deactylation - by [[HDAC]] (Histone Deacetlyase) Deacetylation allows tight arrangement of chromatin, preventing gene expression, while acetylation may occur to open up the chromatin. *[[Methylation]] *[[Phosphorylation]] *[[Ubiquitination]] *[[Ribosylation]] ==See also== *[[Histone]] *[[Histone-Modifying_Enzymes]] ==References== * {{cite journal |author=Jenuwein T, Allis C |title=Translating the histone code |journal=Science |volume=293 |issue=5532 |pages=1074–80 |year=2001 |pmid=11498575 |doi=10.1126/science.1063127}} * {{cite journal |author=Strahl B, Allis C |title=The language of covalent histone modifications |journal=Nature |volume=403 |issue=6765 |pages=41–5 |year=2000 |pmid=10638745 |doi=10.1038/47412}} [[Category:Epigenetics]] {{cell-biology-stub}} [[de:Histon-Code]] [[es:código de histonas]]