Insulators and the Loop Domain Model
In the loop domain model, inactive DNA is heterchromatin, with methylated DNA and hypoacetylated histones. Active DNA, is euchromatin, and has hyperacetylated histones and unmethylated DNA. Chromatin fibers are attached within the nucleus to nuclear matrix component structures through specific DNA binding proteins. This creates ‘loop domains’ within the nucleus, as it compartmentalizes sections of the DNA into exposed regions versus structurally bound DNA that is inaccessible.
It is believed and currently slowly being supported that an enhancer in one of the loop domains, is unable to interact with a promoter in another loop domain. An enhancer is a DNA sequence that is capable of igniting transcription when placed upstream or downstream of a gene. Approximation of the enhancer with the gene is essential. Enhancers are known to be capable of working at 100’s of base pairs away from a gene, and even if they are inverted in orientation.