Histone methylation

Histone methylation is the modification of certain amino acids in a histone protein by the addition of one, two, or three methyl groups. In the cell nucleus, DNA is wound around histones. Methylation and demethylation of histones turns the genes in DNA "off" and "on", respectively, either by loosening their tails, thus, allowing transcription factors and other proteins to access the DNA or by encompassing their tails around the DNA, thus, restricting access to the DNA. This is true in most cases.

Function
This modification alters the properties of the nucleosome and affects its interactions with other proteins.


 * Histone methylation is generally associated with transcriptional repression.
 * However, methylation of some lysine and arginine residues of histones results in transcriptional activation. Examples include methylation of lysine 4 of histone 3 (H3K4), and arginine (R) residues on H3 and H4.