Mechanism of action of insulator
The role of the insulator is directional, which was found in fruit fly experiments. The insertion of the transposon gypsy on the yellow locus y of D. melanogaster causes inactivation of the y gene in some tissues, but the y gene is still active in some tissues because the end of the transposon gypsy There is an insulator sequence. When gypsy is inserted at a different position in the "/ locus, there is a different effect on the activity of the gene.
This is because the activity of the y gene is regulated by four enhancers, and when the insulator is inserted just upstream of the promoter, it blocks the activation of the gene in the wing blade and body cuticle tissues (from the upstream). The enhancer), but does not block the expression of the y gene (from downstream enhancers) in bristles and farsal claws.
Since some enhancers are located upstream of the promoter and some are downstream, the effect of the insulator does not depend on the relative position of the insulator to the promoter. Therefore, the cause of the directionality of the insulator effect has not really been clarified. It has now been found that two loci affect the function of the insulator in a transactivation manner. The nuclear protein encoded by the gene S2J (Hw) recognizes the insulator, and the insulator has an insulating effect after being combined with it. When the gene is mutated, although an insulator is inserted into the y locus, the insulation is lost and y is expressed in all tissues.
Another locus is mod (mdg 4). After mutation, the effect of this gene is opposite to that of Su(Hw), that is, these mutants enhance the insulation and expand the insulation effect of the insulator without directionality. That is, blocking the effects of enhancers on both the upstream and downstream sides. There is an explanation that the first is Su (Hw) combined with the insulator DNA, so that the insulator has an insulating effect. Mod(mdg4) combines with Su(Hw) to lose the insulation effect of the insulator; the mutated mod(mdg4) cannot be combined with Su(Hw), so the insulator enhances the insulation.
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