title: The insulation of genes from external enhancers and silencing chromatin.
abstract: Insulators are DNA sequence elements that can serve in some cases as barriers to protect a gene against the encroachment of adjacent inactive condensed chromatin. Some insulators also can act as blocking elements to protect against the activating influence of distal enhancers associated with other genes. Although most of the insulators identified so far derive from Drosophila, they also are found in vertebrates. An insulator at the 5' end of the chicken beta-globin locus marks a boundary between an open chromatin domain and a region of constitutively condensed chromatin. Detailed analysis of this element shows that it possesses both enhancer blocking activity and the ability to screen reporter genes against position effects. Enhancer blocking is associated with binding of the protein CTCF; sites that bind CTCF are found at other critical points in the genome. Protection against position effects involves other properties that appear to be associated with control of histone acetylation and methylation. Insulators thus are complex elements that can help to preserve the independent function of genes embedded in a genome in which they are surrounded by regulatory signals they must ignore.
authors.affiliation: Laboratory of Molecular Biology, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD 20892-0540, USA.
authors.forename: Bonnie
authors.initials: B
authors.lastname: Burgess-Beusse
authors.forename: Catherine
authors.initials: C
authors.lastname: Farrell
authors.forename: Miklos
authors.initials: M
authors.lastname: Gaszner
authors.forename: Michael
authors.initials: M
authors.lastname: Litt
authors.forename: Vesco
authors.initials: V
authors.lastname: Mutskov
authors.forename: Felix
authors.initials: F
authors.lastname: Recillas-Targa
authors.forename: Melanie
authors.initials: M
authors.lastname: Simpson
authors.forename: Adam
authors.initials: A
authors.lastname: West
authors.forename: Gary
authors.initials: G
authors.lastname: Felsenfeld
mesh_terms: D000818:Animals; D002843:Chromatin / Q000235:genetics*; D004742:Enhancer Elements, Genetic; D020868:Gene Silencing; D006801:Humans
chemical_list: D002843:Chromatin