Some enhancers are located upstream of the promoter, while others are located downstream, so the effect of the insulator does not depend on its relative position with the promoter. Therefore, the reason for the directionality of the insulator effect has not been truly understood. At present, two loci have been found to affect the function of insulators through trans activation. The Nucleoprotein encoded by gene S2J (Hw) recognizes the insulator, and the insulator has insulation effect only after it is combined with it. When the gene mutates, although an insulator is inserted into the y locus, it loses its insulation effect and y is expressed in all tissues. The other locus is mod (mdg4). After the mutation of this gene, its effect is just opposite to Su (Hw), that is, these Mutant types enhance the insulation effect, making the insulation effect of insulators no longer directional and expanding, that is, blocking the effect of enhancers on both upstream and downstream sides. One explanation is that Su (Hw) first binds to the insulator DNA, resulting in an insulation effect on the insulator. The combination of mod (mdg4) and Su (Hw) causes the insulator to lose its insulation effect; The mutated mod (mdg4) cannot bind to Su (Hw), thus enhancing the insulation effect of the insulator.