We have focused attention on the 1.2 kb insulator DNA sequence at the 5 end of the chicken beta-globin locus, and elements upstream of it. This insulator is capable both of blocking the influence of outside enhancers and of preventing the encroachment of condensed chromatin that might shut down expression of the entire region. We have shown previously that enhancer blocking activity is associated with binding of a single protein, CTCF, to a site within the enhancer. We have shown that this protein is responsible for regulation of imprinted gene expression at several imprinted loci. In order to understand the mechanism of action of CTCF we have continued to extend our earlier studies showing that CTCF molecules interact with co-factors. Among the interactions now under investigation is the interaction of CTCF with the cohesin protein complex, recently shown in the laboratories of Matthias Merkenschlager and others to be essential to the recruitment of cohesin to DNA at some stages of the cell cycle. Our recent results have identified SA2 as the cohesin subunit that directly interacts with CTCF, and also identified the domain of CTCF with which it interacts. We have also used mass spec analysis to detect other co-factors that appear to be important for CTCF insulator function. Using these techniques, we have identified a novel and important co-factor of CTCF, the regulatory protein p68. We have shown that this protein, together with its associated RNA co-factor,binds to CTCF, is present genome-wide at CTCF occupies sites on chromatin, and is essential for insulator activity. We also have evidence that at least one role of p68/SRA is to help stabilize the CTCF/cohesin interaction.

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Jian, Xing; Felsenfeld, Gary (2018) Insulin promoter in human pancreatic ? cells contacts diabetes susceptibility loci and regulates genes affecting insulin metabolism. Proc Natl Acad Sci U S A 115:E4633-E4641
Ghirlando, Rodolfo; Felsenfeld, Gary (2016) CTCF: making the right connections. Genes Dev 30:881-91
Wongtrakoongate, Patompon; Riddick, Gregory; Fucharoen, Suthat et al. (2015) Association of the Long Non-coding RNA Steroid Receptor RNA Activator (SRA) with TrxG and PRC2 Complexes. PLoS Genet 11:e1005615
Xiao, Tiaojiang; Wongtrakoongate, Patompon; Trainor, Cecelia et al. (2015) CTCF Recruits Centromeric Protein CENP-E to the Pericentromeric/Centromeric Regions of Chromosomes through Unusual CTCF-Binding Sites. Cell Rep 12:1704-14
Sutiwisesak, Rujapope; Kitiyanant, Narisorn; Kotchabhakdi, Naiphinich et al. (2014) Induced pluripotency enables differentiation of human nullipotent embryonal carcinoma cells N2102Ep. Biochim Biophys Acta 1843:2611-9
Felsenfeld, Gary (2014) A brief history of epigenetics. Cold Spring Harb Perspect Biol 6:
Ghirlando, Rodolfo; Felsenfeld, Gary (2013) Chromatin structure outside and inside the nucleus. Biopolymers 99:225-32
Felsenfeld, Gary; Dekker, Job (2012) Genome architecture and expression. Curr Opin Genet Dev 22:59-61
Ghirlando, Rodolfo; Giles, Keith; Gowher, Humaira et al. (2012) Chromatin domains, insulators, and the regulation of gene expression. Biochim Biophys Acta 1819:644-51
Xiao, Tiaojiang; Wallace, Julie; Felsenfeld, Gary (2011) Specific sites in the C terminus of CTCF interact with the SA2 subunit of the cohesin complex and are required for cohesin-dependent insulation activity. Mol Cell Biol 31:2174-83

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