Enhancers:

While  several  positive  control  components  lie  close  to the  gene  they  regulate additional can be situated long distances away (sometimes 10-50 kb) either upstream or downstream  of the gene shown in the figure. A long-distance  positive control sequence of this  type  is  known as  an  enhancer  if  the  transcription  factor(s)  which  binds  to  it increases the rate of transcription.  An enhancer is classically 100-200 bp long and contains various sequence elements which act together to give the whole enhancer activity.  When they were first found, enhancers were viewed as a distinct class of control component in which they:

-   over long distances can activate transcription;

-   it can be located downstream or upstream of the gene being controlled;

-   are active in moreover orientation with respect to the gene.

Moreover, it is now clear in which some upstream promoter enhancers and elements show strong similarities functionally and physically so which the distinction is not as clear as was once thought. For the enhancers  located a long distance away from the gene being controlled, interaction among transcription  factors bound to the enhancer and to promoter parts  near the gene should occur through looping out of the DNA among the two groups of elements.