Binding of RAREs by R1A-RARα/RXRα heterodimer. (A) Binding of R1A-RARα/RXRα heterodimer to a series of RAREs. The equivalent amounts of in vivo–expressed R1A-RARα/RXRα (top panel) or R1A-RARα(ΔRIIa)/RXRα (bottom panel) proteins were incubated with the radiolabeled RARE probes for DNA-binding assays. Gel-shift assays using α2RARE (B) or p21 RARE (C) hot probes were performed with in vivo–expressed R1A-RARα protein without or with the increasing amount of in vivo–expressed RXRα protein.