Regulation of Transcription in Mammals" Enhancer / Promoter interactions

An Enhancer region 100s of bp upstream from the 5’ Promoter region of the target gene are folded into contact with each other by formation of a chromosome loop. This initiates mRNA synthesis by RNA polymerase II (RNAPol II) bound to the Promoter at the transcription start site of the gene. The structure is stabilized by multiple proteins that form dimers (red zigzags) between the Enhancer and Promoter. Regulatory transcription factors bind to particular DNA sequence motifs in the Enhancer. Transcription factors also bind to the Promoter.

    When a transcription factor in the Enhancer is activated by a signal (For example, phosphorylation as shown by a small red star), the Enhancer activates its target Promoter. The active Enhancer is transcribed by RNAPol II molecules as eRNA molecules off each strand of DNA, oriented in opposite 5'  3' directions. A Mediator (coactivator) complex comprising about 26 proteins in an interacting structure) communicates regulatory signals from the Enhancer DNA-bound transcription factors to the Promoter.