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 The internal structure of Glass porcelain insulators:
About several hundred nucleotides is usually located in the promoter Far regulatory elements (enhancer) or negative regulatory factors (for different chromatin) between a regulatory sequence. Insulator itself the expression of the gene is neither positive effect, and there is no negative effect, and its role is just do not let the effect of other regulatory elements of gene activation or inactivation effect effect.
The role of the insulator is directional, which is found in the fruit fly Drosophila melanogaster. Drosophila (D.melanogaster) yellow locus y transposon insertions gypsy will cause some organizations Y gene inactivation, but some organizations y gene was still active, the reason is that one end of the transposon gypsy an insulator sequence. Have different effects on the activity of the gene when the gypsy inserted in different positions of the "/ loci. This is because the the y gene's activity by 4 enhancer regulation, when the insulator is inserted just upstream of the promoter, blocking the activation of genes in the organization of the winged shoulder (wing blade) and somatic epithelial (body cuticle) (from the upstream enhancer), but do not block the organization of setae (bristles) and tarsal foot (farsal claws) y gene expression (from the downstream enhancer).
Since some enhanced promoter is located upstream of the promoter, some located downstream, so the effect of the insulator does not depend on the relative position of the insulator with the promoter. Directional insulator effect has not really clear. It has been found that there are two loci in trans activation way affect the functionality of the insulator. Nucleoprotein identification of the encoding gene S2J (Hw) insulator, insulators combined with its after insulating effect. When the gene is mutated, the y locus inserted into the insulator, but lost an insulating effect, y is expressed in all tissues. Another locus is mod (mdg 4), after the gene is mutated, and its effect coincides with Su (Hw) opposite, i.e. these mutant enhanced insulation, so that the insulating effect of the insulator no directional extension , that is, blocking the effect of the upstream and downstream sides of the enhancer elements. An interpretation that the first Su (Hw) with insulators DNA binding, the insulator with an insulating effect. mod (mdg4) in conjunction with the Su (Hw), loses its insulating effect of the insulator; mod (mdg4) mutations can not be combined with Su (Hw), So the glass porcelain insulators and enhanced insulation.