Insulator (genetics)
As insulators or insulator elements (English insulators or boundary elements, interface elements) can be referred to in the genetics of eukaryotes DNA sequences defining the regions of the gene expression by various genetic control elements define as enhancer and promoter from each other and insulate it. Example, you can prevent transcription factors from activating the genes that lie upstream, so that they are only able to act downstream. Insulators act by DNA binding proteins which are specific for their sequence. And delimiting two distinct from enhancers characteristics are a function of the position, and a phenomenon which is referred to as insulator bypass. An insulator has to fulfill his function, be positioned between an enhancer and a promoter. If two insulators are located next to each other so their insulating characteristics overcome (hence bypass).
Their influence on genes that are imprinted, also makes them a part of epigenetic regulatory mechanisms.
Insulator types
There are two types of isolators have two different effects:
Enhancer -blocking insulators ( enhancer blocking insulators ) are DNA elements placed between an enhancer and a promoter can prevent the interaction between these two. This differs from the repressors, which act both on the upstream and on the downstream lying promoter. Models suggest that two insulators via associated DNA - binding factors form loops in chromatin.
Barrier - insulators ( insulators barrier ), however, protect genes against the repressing effect of heterochromatin. They suppress position effect variegation ( PEV ). Heterochromatin is in contrast to euchromatin kondensiertere a form of chromatin, which is achieved by specific histone modifications. In heterochromatin are only a few genes, and these are often not highly expressed. The DNA is methylated in heterochromatin in plants and in vertebrates particularly strong at CpG islands. The heterochromatin has the characteristic of a repressive act on lying adjacent euchromatic genes. The strength of this repression may vary from cell to cell, thereby forming a mosaic structure generated in the level of expression of the affected gene. This mosaic expression is referred to as position effect variegation.
History
The properties of the enhancer -blocking insulators were described in the 1980s in Drosophila melanogaster. With genetic work with the gypsy retrotransposon the group found to Pamela Geyer at the University of Baltimore, that gypsy activity more remote enhancer blocked.
The first insulator element in vertebrates was described in 1993 and named cHS4. Only this time, established the concept of the insulator. To the sequence of a zinc finger protein binds cHS4 CTCF called that plays a role in the imprinting of Igf2.