H3K4me1 is an epigenetic modification to the DNA packaging protein Histone H3. It is a mark that indicates the mono-methylation at the 4th lysine residue of the histone H3 protein and often associated with gene enhancers. H3K4me1 is enriched at active and primed enhancers. Transcriptional enhancers control the cell-identity gene expression and are important in the cell identity.