The function of ceramic insulator is directional

The function of insulator is directional, which is found in the experiment of fruit fly. The insertion of the transposon Gypsy into the yellow locus y of Drosophila (D. melanogaster) will inactivate the Y gene in some tissues, but the Y gene is still active in some tissues. The reason is that there is an insulator sequence at one end of the transposon gypsy. When Gypsy is inserted at different positions of the locus, it has different effects on gene activity. This is because the activity of Y gene is regulated by four enhancers. When the insulator is inserted just upstream of the promoter, it blocks the activation of Y gene in wing blade and body cuticle tissues (from the upstream enhancer), but does not block the expression of Y gene in bristles and far claws tissues (from the downstream enhancer). Since some enhancers are located upstream and some downstream of the promoter, 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 insulator effect has not been really understood. At present, it has been found that two loci affect the function of insulators by 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 was mutated, although an insulator was inserted into the Y locus, it lost its insulating effect, and y was expressed in all tissues. Another locus is mod (MDG 4). After the mutation of this gene, its effect is just opposite to su (HW), that is, these mutants enhance the insulation effect, so that the insulation effect of insulator is no longer directional and expanded, that is, blocking the effect of enhancers on both upstream and downstream sides. One explanation is that Su (HW) first binds to insulator DNA to make insulator have insulation effect. The combination of mod (MDG4) and su (HW) makes the insulator lose the insulation effect; The abrupt mod (MDG4) cannot be combined with Su (HW), so the insulator enhances the insulation effect.