hCAR-REF and hCAR-4aaINS bind to the CYP2B6 PBREM NR1 and NR2 elements. EMSA studies were performed using recombinantly expressed proteins (A). (B) GST alone did not bind the respective DNA elements (lane 1, top and bottom gel). All hCAR isoforms appeared to interact with the tested DNA elements in the absence of RXRα, forming a more rapidly migrating complex (lanes 2, 3, 4 and 5). This effect was more pronounced with the NR2 element. RXRα bound weakly to the NR1, but not the NR2 element (lane 6, top gel). The hCAR-REF–RXRα complex bound to both of the previously characterized hCAR response elements (lane 7, top and bottom gels). The hCAR-4aaINS–RXRα complex also bound to both elements, although this interaction appeared to be weaker when compared with the hCAR-REF complex. In the top gel, it appears that the hCAR-dblINS–RXRα complex bound DNA (lane 10, top gel); however, subsequent attempts to reproduce this result were unsuccessful.