H3K9me2

H3K9me2 is an epigenetic modification to the DNA packaging protein Histone H3. It is a mark that indicates the di-methylation at the 9th lysine residue of the histone H3 protein. H3K9me2 is strongly associated with transcriptional repression.^[1][2][3] H3K9me2 levels are higher at silent compared to active genes in a 10kb region surrounding the transcriptional start site.^[4] H3K9me2 represses gene expression both passively, by prohibiting acetylation^[5] as therefore binding of RNA polymerase or its regulatory factors, and actively, by recruiting transcriptional repressors.^[6][7] H3K9me2 has also been found in megabase blocks, termed Large Organised Chromatin K9 domains (LOCKS), which are primarily located within gene-sparse regions but also encompass genic and intergenic intervals.^{[8][9][10][11]} Its synthesis is catalyzed by G9a, G9a-like protein, and PRDM2.^[1][3][12] H3K9me2 can be removed by a wide range of histone lysine demethylases (KDMs) including KDM1, KDM3, KDM4 and KDM7 family members.^[13][6] H3K9me2 is important for various biological processes including cell lineage commitment,^[10][14] the reprogramming of somatic cells to induced pluripotent stem cells,^[15] regulation of the inflammatory response,^[16][17] and addiction to drug use.^{[2][18][19][20]}