Figure 2

The unusual DNA structure formed by CTCF at the β-globin FII insulator element is directional. (A) Schematic diagram of the DNA bending vector pBEND2 containing the FII insulator element in the reverse orientation, as indicated by the leftward-pointing arrowhead. The FII site is inserted between two XbaI sites (X). Digestion of the vector with MluI (M), BglII (Bg), NheI (N), SpeI (Sp), EcoRV (E), SmaI (Sm), KpnI (K) and BamHI (Ba) results in the generation of 166 bp probes. The FII site is permuted from the right (M) to the left end of the fragment (Ba), as indicated below the sequence. Each probe contains the FII element at a different position in the reverse orientation. (B) The assays were done as in Figure 1B using ³²P-labelled, permuted probes generated from the vector pBEND2-FII-Reverse Orientation. Note that the mobilities of the CTCF-DNA complexes are the mirror image of those observed with the pBEND2-FII-Forward vector (Figure 1B).