The Principle Of Tempered Glass Insulators

Some enhancers are located upstream of the promoter, while others are downstream, so the insulator's effect does not depend on its relative position to the promoter. Therefore, the reason for the directionality of the insulator's effect is not yet fully understood. Currently, two loci have been found to affect insulator function through trans-activation. The S2J(Hw) gene encodes a nucleoprotein that recognizes insulators; the insulator only exerts its insulating effect after binding to it. When this gene mutates, although an insulator is inserted into the y locus, the insulating effect is lost, and y is expressed in all tissues. The other locus is mod(mdg 4), and mutations in this gene have the opposite effect to Su(Hw); these mutants all enhance the insulating effect, making the insulator's insulating effect no longer directional but extended, thus blocking the effects of the upstream and downstream enhancers. One explanation is that Su(Hw) first binds to the insulator DNA, giving the insulator its insulating effect. When mod(mdg4) combines with Su(Hw), the insulator loses its insulating effect; when mod(mdg4) changes abruptly, it cannot combine with Su(Hw), thus the insulator's insulating effect is enhanced again.