CCCTC Binding Factor (CTCF)

CTCF is a major protein involved in insulator activity. The protein CTCF plays heavily in the role of repressing the insulin-like growth factor 2 gene, by binding to the H-19 imprinting control region (ICR) along with Differentially-methylated Region-1 (DMR1) and MAR3.Binding of targeting sequence elements by CTCF can block the interaction between enhancers and promoters, therefore limiting the activity of enhancers to certain functional domains. Besides acting as enhancer blocking, CTCF can also act as a chromatin barrier by preventing the spread of heterochromatin structures.In 2007, two independent studies (Xie et al. from MIT and Kim et al. from UCSD) revealed that the human genome contains nearly 15,000 CTCF insulator sites, suggesting a widespread role of CTCF in gene regulation.