Histone methylation is the addition of methyl groups (-CH3) to histone proteins, usually to lysine (and sometimes arginine) amino acids in the histone tails. The methyl groups are added by enzymes called histone methyltransferases and removed by histone demethylases.How it differs from acetylation
Unlike acetylation, methylation does not remove the positive charge on lysine. Instead, the methyl groups act as signals that are recognised by other proteins. These proteins either help to pack the chromatin tightly or help to open it up.The effect depends on where the methyl group is
Whether histone methylation switches a gene on or off depends on which amino acid is methylated and how many methyl groups are added (one, two or three).
• Methylation of some lysines attracts proteins that condense the chromatin into heterochromatin, so genes are silenced.
• Methylation of other lysines is found near the promoters of genes being actively transcribed, and helps to keep the chromatin as euchromatin.Working with other marks
Histone methylation often works together with DNA methylation. For example, proteins that bind methylated DNA can attract histone methyltransferases, and the resulting histone methylation reinforces the silencing of the gene. Together these marks keep genes switched off in a stable way through many cell divisions, which is important for keeping differentiated cells specialised.Histone methylation is generally more stable than histone acetylation, which is added and removed quickly.
Unlike acetylation, methylation does not remove the positive charge on lysine. Instead, the methyl groups act as signals that are recognised by other proteins. These proteins either help to pack the chromatin tightly or help to open it up.The effect depends on where the methyl group is
Whether histone methylation switches a gene on or off depends on which amino acid is methylated and how many methyl groups are added (one, two or three).
• Methylation of some lysines attracts proteins that condense the chromatin into heterochromatin, so genes are silenced.
• Methylation of other lysines is found near the promoters of genes being actively transcribed, and helps to keep the chromatin as euchromatin.Working with other marks
Histone methylation often works together with DNA methylation. For example, proteins that bind methylated DNA can attract histone methyltransferases, and the resulting histone methylation reinforces the silencing of the gene. Together these marks keep genes switched off in a stable way through many cell divisions, which is important for keeping differentiated cells specialised.Histone methylation is generally more stable than histone acetylation, which is added and removed quickly.