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H3K4me3 denotes a specific chemical modification of proteins used to package DNA in eukaryotic cells (including human cells). The proteins, known as histones, are major components of chromosomes. This modification is commonly associated with active transcription of nearby genes.
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Nomenclature
H3K4me3 means trimethylation of lysine 4 on histone H3 protein subunit:
Epigenetic marker
A lysine specific histone methyltransferases (HMT) transfers three methyl groups to histone H3. H3K4me3 is used as a histone code or histone mark in epigenetic studies (e.g., chromatin immunoprecipitation ChIP-seq) to identify active gene promoters. H3K4me3 histone modification is found in high abundance in the cells. H3K4me3 is highly enriched at active promoters near transcription start sites (TSS).
Lysine methylation
The following diagram shows 3 methyl groups (—CH3) added to lysine, replacing hydrogen atoms:
Incremental methylation of lysine residue (dashed line denotes peptide backbone):
H3K4me3 modification corresponds to the rightmost diagram, above trimethyllysine label.