The mechanism underlying enhancer-blocking by insulators is unclear. We explored the activity of human β-globin HS5, the orthologue of the CTCF-dependent chicken HS4 insulator. An extra copy of HS5 placed between the β-globin locus control region (LCR) and downstream genes on a transgene fulfills the classic predictions for an enhancer-blocker. Ectopic HS5 does not perturb the LCR but blocks gene activation by interfering with RNA pol II, activator and coactivator recruitment, and epigenetic modification at the downstream β-globin gene. Underlying these effects, ectopic HS5 disrupts chromatin loop formation between β-globin and the LCR, and instead forms a new loop with endogenous HS5 that topologically isolates the LCR. Both enhancer-blocking and insulator-loop formation depend on an intact CTCF site in ectopic HS5 and are sensitive to knock-down of the CTCF protein by siRNA. Thus, intrinsic looping activity of CTCF sites can nullify LCR function.
Physical interactions between genetic elements located throughout the genome play important roles in gene regulation and can be identified with the Chromosome Conformation Captu...
Macrosatellite DNA is composed of large repeat units, arranged in tandem over hundreds of kilobases. The macrosatellite repeat DXZ4, localized at Xq23-24, consists of 50–100 cop...
Establishment and segregation of distinct chromatin domains are essential for proper genome function. The insulator protein CCCTC-binding factor (CTCF) is involved in creating b...
Insulators are DNA elements that prevent inappropriate interactions between the neighboring regions of the genome. They can be functionally classified as either enhancer blocker...
Abstract Insulators are specialized DNA sequences that prevent enhancer-activated transcription only when interposed between an enhancer and its target promoter. The Drosophila ...
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