Figure 2.

A model of the eukaryotic transcriptional unit. For active gene transcription to take place, transcription factors bind to active promoter (red) and enhancer (orange, yellow) regions. Promoter-enhancer units are separated by insulator sites (depicted in blue). Insulators sites are enriched for CTCF binding, and active promoters can be identified by H3K4me2/3 enrichment. Poised promoter regions are enriched in both H3K4me3 and H3K27me3 histone modification. Enhancers can be upstream or downstream of promoters, and they are enriched for H3K4me1, H3K27ac, and H3K9ac.