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Histone methylation is a principal epigenetic modification of chromatin [9] that determines gene expression, genomic stability, stem cell maturation, cell lineage development, genetic imprinting, DNA methylation, and cell mitosis. [2] Front view of the human enzyme Histone Lysine N-Methyltransferase, H3 lysine-4 specific.
Front view of the human enzyme Histone Lysine N-Methyltransferase, H3 lysine-4 specific. The genome is tightly condensed into chromatin, which needs to be loosened for transcription to occur. In order to halt the transcription of a gene the DNA must be wound tighter. This can be done by modifying histones at certain sites by methylation.
These histone marks can serve as docking sites of other co-activators as seen with H3K27me3. This occurs through polycomb mediated gene silencing via histone methylation and chromodomain interactions. A polycomb repressive complex (PRC); PRC2, mediates the tri-methylation of histone 3 on lysine 27 through histone methyl transferase activity. [5]
The H3K4me3 modification is created by a lysine-specific histone methyltransferase (HMT) transferring three methyl groups to histone H3. [6] H3K4me3 is methylated by methyltransferase complexes containing a protein WDR5 , which contains the WD40 repeat protein motif . [ 7 ]
Histone methyltransferases are critical for genetic regulation at the epigenetic level. They modify mainly lysine on the ε-nitrogen and the arginine guanidinium group on histone tails. Lysine methyltransferases and Arginine methyltransferases are unique classes of enzymes, but both bind SAM as a methyl donor for their histone substrates ...
Transcriptional enhancers control the cell-identity gene expression and are important in the cell identity. Enhancers are primed by histone H3K4 mono-/di-methyltransferase MLL4 and then are activated by histone H3K27 acetyltransferase p300. [5] H3K4me1 fine-tunes the enhancer activity and function rather than controls. [4]
Euchromatic histone-lysine N-methyltransferase 2 (EHMT2), also known as G9a, is a histone methyltransferase enzyme that in humans is encoded by the EHMT2 gene. [5] [6] [7] G9a deposits the mono- and di-methylated states of histone H3 at lysine residue 9 (i.e., H3K9me1 and H3K9me2) and lysine residue 27 (H3K27me1 and H3K27me2).
The lysine residue is converted to N 6-methyllysine residue. Leftmost: side chain of lysine. Next: N 6-methyllysine side chain. This histone modification is often abbreviated H4K20me1: H4 - type of histone; K - symbol of lysine; 20 - position of the lysine residue modified; me - abbreviation for methyl group; 1 - number of methyl groups transferred