H3K9me2

H3K9me2, short for Histone H3 Lysine 9 di-methylation, is a histone modification associated with transcriptional repression and heterochromatin formation in eukaryotes. Specifically, it refers to the dimethylation of lysine residue 9 on the histone H3 protein.

Histones are proteins around which DNA is wrapped to form chromatin, the complex of DNA and protein that makes up chromosomes. Modifications to histones, such as methylation, acetylation, phosphorylation, and ubiquitylation, can alter chromatin structure and accessibility, influencing gene expression.

The methylation of lysine residues is catalyzed by histone methyltransferases (HMTs). In the case of H3K9me2, enzymes like G9a/EHMT2 and GLP/EHMT1 are responsible for adding the two methyl groups to the lysine 9 residue.

H3K9me2 serves as a binding platform for heterochromatin protein 1 (HP1), a key protein involved in the formation and maintenance of heterochromatin. The interaction between H3K9me2 and HP1 promotes chromatin compaction and the silencing of genes within heterochromatic regions.

The levels and distribution of H3K9me2 can vary depending on the cell type, developmental stage, and environmental conditions. Dysregulation of H3K9me2 has been implicated in various diseases, including cancer and developmental disorders. It is often found at repetitive DNA sequences, such as those found in centromeres and telomeres, contributing to their structural integrity and silencing.