The RIIa domain-mediated protein interaction of R1A-RARα/R1A-RARα and R1A-RARα/R1A. The 293T cells were transiently transfected with the following combined expression vectors: (A) M2-R1A-RARα + Myc-R1A-RARα, M2-R1A-RARα + Myc-R1A-RARα(ΔRIIa), M2-R1A-RARα + Myc-R1A, M2-R1A-RARα + Myc-PLZF-RARα, or M2-R1A-RARα + Myc-PAX5; (B) M2-R1A-RARα + HA-R1A-RARα, M2-R1A-RARα + HA-R1A, M2-R1A-RARα + HA-R1A-RARα(ΔRIIa), or M2-R1A-RARα + HA-containing empty vector; (C) M2-R1A + Myc-R1A-RARα, M2-R1A + Myc-R1A-RARα(ΔRIIa), or M2-R1A + Myc-R1A, as indicated. The white star represents the position of mouse IgG. Cell lysates were separated by SDS-PAGE directly (Input) or after immunoprecipitation using antibody against the M2-FLAG epitope (immunoprecipitation, IP) and subsequently immunoblotted using antibody against Myc or HA epitope. The protein-protein interactions between R1A-RARα fusion protein and wild-type R1A were analyzed using mammalian 2-hybrid assay (D-F). The AD (activation domain) alone or its fusion with R1A-RARα, R1A-RARα(ΔRIIa), or R1A was expressed in HeLa cells together with a luciferase reporter containing 4 copies of Gal4-binding sites (4xUAS-TK luc) as well as Gal4 DBD-fused R1A-RARα (BD-R1A-RARα) (D), Gal4 DBD-fused R1A (BD-R1A) (E), or Gal4 DBD-fused R1A-RARα(ΔRIIa) (BD-R1A-RARα(ΔRIIa)) (F). The relative luciferase activities are averages of 3 independent transfection experiments normalized to β-galactosidase activity.