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. Author manuscript; available in PMC: 2009 Dec 1.
Published in final edited form as: Stem Cells. 2008 Sep 11;26(12):3257–3266. doi: 10.1634/stemcells.2008-0258

Figure 1.

Figure 1

Schematic diagram of the chicken β-globin gene locus (left) and the human T cell receptor (TCR) α/δ locus (right) with the positions of the 5′HS4 and BEAD-1 (BEAD) insulators indicated, respectively. The sequences of the FII and BEAD-A enhancer blocking components comprising the FB element are shown at the bottom. During efforts to identify the protein responsible for enhancer blocking activity (CTCF), Felsenfeld and colleagues previously demonstrated that mutation of a consensus Sp1 site (functionally neutral ‘CC’ to ‘AA’ transversion mutations mentioned in the text) had no effect on CTCF binding or enhancer blocking activity; likewise, these investigators found that deletion of the ‘TAAT’ motif within a sequence having homology to a binding site for the yeast α2 homeodomain repressor protein and which overlaps a partial match to the binding site of the Drosophila suppressor of Hairy-wing protein, had no effect on CTCF binding or enhancer blocking activity. Abbreviations: FR, folate receptor gene; LCR, locus control region; OR, odorant receptor gene. Adapted from refs. [18, 37, 38]. See text for details.