The role of insulators is directional, which was found in the fruit fly experiment. Fruit flies (D. Melanogaster) yellow loci on y into the transposon gypsy, cause y gene inactivation of some organizations, but some y gene is still active in the organization, its reason lies in the transposon gypsy an insulator sequence at one end. When gypsy is inserted at different locations of the locus, there are different effects on gene activity. This is because the y gene activity is regulated by the four enhancer, when the insulator is inserted in the upstream of the promoter, the wing shoulder (wing blade) and body epithelium (body cuticle) tissue block gene activation (from upstream enhancer), but not blocking in bristles (bristles) and fu (farsal claws) y gene expression in tissue (from downstream enhancer).
Since some of the enhancers are upstream of the promoter and some are downstream, the effect of the insulator does not depend on the relative position of the insulator with the promoter. Therefore, the reason for the direction of insulator effect is not really understood. It has been found that there are two locus which affect the function of insulators in the form of reverse activation. The nuclear protein identification insulator (Hw) encoded by the suspended high pressure glass toughened insulator gene S2J(Hw) is used to insulate the insulator after its combination. When the gene was mutated, the insulator was inserted in the y locus, but the insulation was lost, and y was expressed in all tissues. Another loci is mod (MDG 4), the gene mutated, after its effect is just the reverse of Su (Hw), namely the type of these mutations are to enhance the insulation effect, make the insulation of the insulator effects no longer have directional and expanded, which is blocking the upstream and downstream sides to enhance the effect of the son. One explanation is that the insulator has an insulating effect after the combination of the Su(Hw) and insulator DNA. The mod(mdg4) combines with the Su(Hw) to insulate the insulator from the insulation effect; The mutated mod(mdg4) cannot be combined with the Su(Hw), so the insulator enhances the insulation.