Deletion of the RAR C terminus enhances binding to SMRT. Full-length wild-type RARα (wt-RAR) or a C-terminal truncation (RAR-403t) were synthesized as radiolabeled proteins by transcription and translation in vitro and were tested for the ability to bind to nonrecombinant GST, to GST-SMRT RID-1 (SMRT amino acids 1055 to 1291), or to GST-SMRT RID-2 (SMRT amino acids 1291 to 1495) as described in the legend to Fig. Fig.2.2. The assays were performed in the presence (+) or absence (−) of 1 μM all-trans retinoic acid. After washing was done, the receptors remaining bound to the immobilized GST fusion proteins were eluted, resolved by SDS-PAGE, and visualized and quantified by PhosphorImager analysis. The amount of a radiolabeled receptor bound to a GST fusion polypeptide is presented as a percentage of the total radiolabeled receptor (input) used in each binding reaction. The averages and standard deviations of at least two experiments are presented.