The TR-FRET RAR (retinoic acid receptor) beta Coactivator Assay Kit provides a sensitive and robust method for highthroughput screening of potential RAR beta ligands as agonists of ligand-dependent coactivator recruitment. The kit uses a terbium (Tb)-labeled anti-GST antibody, a fluorescein-labeled coactivator peptide, and a human recombinant RAR beta ligand-binding domain (RAR beta-LBD) that is tagged with glutathione-S-transferase (GST) in a homogeneous, mix-and-read assay format.

When running the TR-FRET RAR beta coactivator assay in agonist mode to identify agonist compounds, RAR beta-LBD is added to ligand test compounds, followed by addition of a mixture of the fluorescein-coactivator peptide and Tb-labeled anti-GST antibody. After an incubation period at room temperature, the 520 nm/495 nm TR-FRET ratio is calculated and can be used to determine the EC50from a dose response curve of the compound. Based on the biology of the RAR beta-coactivator peptide interaction, this ligand EC50is a composite value representing the amount of ligand required to bind to receptor, effect a conformational change, and recruit coactivator peptide.