H3K4me3 - tri-methylation of lysine 4 of H3. Activating mark. (IHEC reference epigenome). This modification typically occurs at nucleosomes adjacent to the transcription start sites of actively transcribed genes. Aligned ChiP-seq reads for H3K4me3 typically appears as a localized enriched regions size of ~2-4Kb around the TSS, but in the case of some of strongly expressed genes the read coverage can extend further downstream into the gene body. Generally the TSS H3K4me3 signal is proportional to the gene expression with a global spearman correlation for protein coding genes ~0.7. Typically we observe 25-40K of enriched H3K4me3 locations (in humans).
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