Formation of line insulators
Some enhancers are located upstream of the promoter and some are located downstream, so the effect of the insulator does not depend on the relative position of the insulator and the promoter.
Therefore, the reason for the directionality of the insulator effect has not really been clarified. It was found that there are two loci that affect the function of the insulator in a trans-activation manner. The nucleoprotein encoded by the gene S2J (Hw) recognizes the insulator, and the insulator can only insulate after it is combined with it.
When the gene is mutated, although an insulator is inserted in the y locus, the insulating effect is lost, and y is expressed in all tissues. The other locus is mod(mdg 4). After this gene is mutated, its effect is just the opposite of Su(Hw), that is, these mutants all enhance the insulating effect, so that the insulating effect of the insulator is no longer directional and expands , Which is to block the effect of enhancers on both upstream and downstream sides.
There is an explanation that Su (Hw) first combines with the insulator DNA to make the insulator have an insulating effect. The combination of mod (mdg4) and Su (Hw) makes the insulator lose its insulating effect; the abrupt mod (mdg4) cannot be combined with Su (Hw), so the insulator enhances the insulation effect.