Binding of RAREs by R1A-RARα fusion protein homodimer. (A) Binding of R1A-RARα homodimer to a series of RAREs assayed by gel-shift assays. Equivalent amounts of in vivo–expressed R1A-RARα, PML-RARα, NPM-RARα, or RARα/RXRα proteins were incubated with the following radiolabeled RARE probes: the synthetic RARE sequences, DR1G to DR5G, and the RAREs from the natural enhancer/promoter regions of the human RARβ2 (β2RARE), RARα2 (α2RARE), HOXA1, HOXB1, CYP26A1, p21-WAF1, FGF8, and CEBPϵ gene. (B) Gel-shift assays were performed using in vivo–expressed R1A-RARα protein incubated with radiolabeled DR5G (hot probe) without or with unlabeled DR5G (cold probe) in the amounts indicated. (C) Gel-shift assays were performed with α2RARE radiolabeled probe incubated with in vivo–expressed proteins R1A-RARα, R1A-RARα(ΔRIIa), and PML-RARα without or with RXRα as indicated. (D) Gel-shift assay analysis of the equivalent in vitro translation proteins R1A-RARα, R1A-RARα(ΔRIIa), R1A-RARα-M412R/T415R, and R1A-RARα(ΔRIIa)-M374R/T377R alone or plus RXRα, as indicated.