In some cases one of the monomers lacks the DNA-binding helix which prevent efficient binding by the dimer and leads to inactivation. Important techniques for the purification of DNA-binding proteins from higher eucaryotes for which genetic techniques are not possible. Expression cloning using a probe coding for the specific DNA-binding sequence. In eucaryotes transcriptional control is more complex but the same basic principles apply. Gene regulatory proteins act on this complex to modulate the rate of transcription initiation.
Activators increase it while repressors decrease it.
The regulatory proteins tend to bind to adjacent sequences 5 of the TATA box. DNA-looping allows a transcription factor bound at distant enhancer to interact with RNA pol or other basal transcription factors. Enhances usually contain multiple functional sequence elements that bind different factors. These may have activating or suppressing actions on expression. It is through the integration of all these signals that gene expression is controlled during development and differentiation, as well as during the response of cells to hormones and growth factors.