H3K4me3 marks actively transcribed and poised gene promoters inmammals. (A) The genome-wide correlation of mRNA expressionlevels (High, Medium, Low, and Silent) with H3K4me3 levels at human genepromoters. Note that a dip of H3K4me3 levels may be associated with thenucleosome-free region around the transcriptional start site (TSS). Adapted from . (B) The Venn diagram showing the percentage of genesthat have H3K4me3 and/or H3K27me3 in their promoters in mouse and humanES cells. All percentages are based on about total 18,000 genes. The“bivalent” denotes the promoters that contain both H3K4me3and H3K27me3 marks. Adapted from [36, 37, 43].