Aryl hydrocarbon receptor (AhR) is an important ligand-activated transcription factor involved in the regulation of various important physiological functions. AhR can be activated by a variety of signals with different affinities, including xenobiotics and endogenous signals. In the absence of ligand, AhR forms a stable multiprotein complex in the cytosol with the chaperone Hsp90 and co-chaperon p23, XAP2.