Histone methylation is the modification of certain
amino acidsin a histoneprotein by the addition of one, two, or three methylgroups.
This modification alters the properties of the
nucleosomeand affects its interactions with other proteins.
* Histone methylation is generally associated with transcriptional repression.
* However, methylation of some
lysineand arginineresidues of histones results in transcriptional activation. Examples include methylation of lysine 4 of histone 3(H3K4), and arginine (R) residues on H3 and H4.
For many years histone methylation was thought to be a permanent modification. Very recently two families of histone demethylating
enzymes were discovered.
* The first was Lysine Specific Demethylase 1 (
LSD1) which is an flavin-dependent monoamine oxidasewhich can demethylate mono- and di-methylated lysines, specifically histone 3, lysines 4 and 9 (H3K4 and H3K9). This enzyme cannot demethylate tri-methylated lysines and for a short while it was thought that tri-methylated lysines may indeed be permanent modifications.
* In late 2005 the
Jumonji domain-containing (JmjC) histone demethylases were discovered which are able to demethylate mono-, di-, or tri-methylated lysines thereby disproving the theory that histone methylation is permanent once and for all.
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