A given gene may have several different possible enhancer sites. Each enhancer may bind more than one protein factor to increase or decrease transcription. Regulation of transcription is due to proteins bound at the enhancer sites interacting with proteins bound at the promoter. General structure contains a trans-activating domain which may enhance the efficiency of building the transcription complex. There are 3 a -helices in between.
Prolactin is a hormone that stimulates milk production.
This promotes transcription of the prolactin gene. Homodimer doesn't bind well. Ubiquitous bHLH is present in cells as a monomer. Id lacks a DNA-binding region. Helical region where leucines on the monomers interact to form the dimer.