Figure 1.

Cis-regulatory elements and the control of gene transcription. A] Linear diagram of a hypothetical transcribed gene [green arrow] and its promoter [Prom] flanked by two insulator elements [Ins] and two enhancers [Enh]. B] Binding of the chromatin architectural factor CTCF to insulator elements traps the enhancer in a loop away from the gene promoter, inhibiting transcription [red arrow]. C] Following developmental methylation [Me] of insulator elements, which blocks CTCF binding, the enhancer loops over to interact with the promoter, promoting transcription. The active enhancer is marked by H3K27 acetylation [Ac]. D] Upon activity-induced recruitment of transcriptional co-activators, a shadow enhancer is recruited to the gene promoter, further promoting transcription.