Mapping of KIBP-binding sites within the 305-bp regulatory element in vitro. A, Left, in vitro interaction between TRX:BEIL1 and the region 100 to 241 bp of the regulatory element. Right, binding of TRX:BEIL1 to the region 122 to 175 bp. The positions of probes 40 to 42 relative to probes 4 and 5 are indicated. Bases similar to a DNA fragment recognized by EIN3 are in boldface. B, Left, in vitro interaction between TRX:BERF1 and the region 168 to 305 bp of the regulatory element. Right, binding of TRX:BERF1 to the region 200 to 262 bp. The positions of probes 49 to 51 relative to probes 8 and 9 are indicated. C, In vitro interaction between TRX:BGRF1 and the region 236 to 305 bp of the regulatory element, covered by 34-bp probes (left), and the region 257 to 305 bp, covered by 24-bp probes (right). The positions of probes 43 to 45 relative to probes 10 and 11 are indicated. −, Free probe. D, Schematic representation of the 305-bp intronic element. Eleven overlapping 34-bp fragments (1–11) spanning the region from 80 to 305 bp were tested in gel retardation assays. The positions of the KIBP-binding sites are indicated.