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H3K4me3 is used as a histone code or histone mark in epigenetic studies (usually identified through chromatin immunoprecipitation) to identify active gene promoters. H3K4me3 promotes gene activation through the action of the NURF complex, a protein complex that acts through the PHD finger protein motif to remodel chromatin. [2]
During development, TrxG proteins maintain activation of required genes, particularly the Hox genes, after maternal factors are depleted. [8] This is accomplished by preserving the epigenetic marks, specifically H3K4me3, established by maternally-supplied factors. [9]
H3K4me1 is a chromatin signature of enhancers, H3K4me2 is highest toward the 5′ end of transcribing genes and H3K4me3 is highly enriched at promoters and in poised genes. H3K27me3 , H4K20me1 and H3K4me1 silence transcription in embryonic fibroblasts, macrophages, and human embryonic stem cells (ESCs).
Methylated lysines are the best understood marks of the histone code, as specific methylated lysine match well with gene expression states. Methylation of lysines H3K4 and H3K36 is correlated with transcriptional activation while demethylation of H3K4 is correlated with silencing of the genomic region.
The H3K27me3 mark silences the gene while the H3K4me3 mark allows the gene to not be permanently silenced, and activated when needed. [2] Embryonic stem cells and imprinted genes are associated with both activating (H3K4me3) and repressive (H3K27me3) marks, as they allow a gene to be repressed until activation is needed.
For example, trimethylation of histone H3 at lysine 4 is an active mark for transcription and is upregulated in hippocampus one hour after contextual fear conditioning in rats. However, dimethylation of histone H3 at lysine 9 ( H3K9me2 ), a signal for transcriptional silencing, is increased after exposure to either the fear conditioning or a ...
The term "Histone H3" alone is purposely ambiguous in that it does not distinguish between sequence variants or modification state. Histone H3 is an important protein in the emerging field of epigenetics, where its sequence variants and variable modification states are thought to play a role in the dynamic and long term regulation of genes.
This is the case in H3K27ac which is an active enhancer mark. It is found in distal and proximal regions of genes. It is enriched in transcriptional start sites (TSS). H3K27ac shares a location with H3K27me3 and they interact in an antagonistic manner. H3K27me3 is often seen to interact with H3K4me3 in bivalent domains . [11]