Some enhancers are located upstream of the promoter, while others are located downstream, so the effect of the insulator does not depend on the relative position between the insulator and the promoter. Therefore, the reasons for the directionality of insulator effects have not been truly understood. Currently, two gene loci have been found to affect the function of insulators through trans activation. The nucleoprotein encoded by gene S2J (Hw) recognizes insulators, and only when the insulator binds to it can it provide insulation. When the gene mutates, although an insulator is inserted into the y locus, it loses its insulating function and y is expressed in all tissues. Another gene locus is mod (mdg 4), which has a mutation that has the opposite effect to Su (Hw). These mutations enhance the insulation effect, making the insulation effect of the insulator no longer directional and expanding, thus blocking the effects of enhancers on both upstream and downstream sides. One explanation is that Su (Hw) first binds to the DNA of the insulator, causing it to have an insulating effect. Mod (mdg4) combined with Su (Hw) causes the insulator to lose its insulation effect; The mutated mod (mdg4) cannot bind with Su (Hw), so the insulator enhances its insulation effect.