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The chicken
-globin insulator protects a transgene
from epigenetic silencing in a cell culture system. Shown here are two models illustrating possible mechanisms of insulator-mediated protection of transcriptional activity. Paired insulators are shown to
maintain an active chromatin environment over the transgene between
them by excluding transcriptional repressive complexes that include
methyl CpG-binding proteins (M), histone deacetylases (D), or any other
components (top). Alternatively, insulators maintain an
activated chromatin environment by sequestering transcriptional activators, such as histone acetylases (A) within the transgene (bottom). (I) Insulator; (P) promoter; (En) enhancer.
(For details, see Pikaart et al., p. 2852.)