Mapping the 90 kDa heat shock protein binding region of the Ah receptor

Expression of a series of Ah receptor (AhR) deletion mutants in an in vitro translation system has been previously used to map several functional domains of the murine AhR. In this report, quantitative immunoprecipitation of 90-kDa heat shock protein (hsp90) from reticulocyte lysate allowed us to measure the level of the AhR and AhR deletion mutants complexed with hsp90. After translation of a series of deletion mutants it was determined that there are two distinct domains important in forming a stable AhR/hsp90 complex, corresponding to amino acid sequences 1-166 and 289-347 of the AhR. Neither ARNT, nor Per were able to stably interact with hsp90. Thus, the AhR appears to be a unique member of the PAS domain family of proteins that binds a known ligand and stably interacts with hsp90.