Identification of a 120-kDa protein associated with aromatic hydrocarbon receptor nuclear translocator

The aromatic hydrocarbon receptor nuclear translocator (ARNT) is a basic helix-loop-helix-PAS protein which forms a heterodimer with aromatic hydrocarbon receptor (AHR), this heterodimer mediating the signal transduction in response to the various xenobiotics such as 2,3,7,8-tetrachlorodibenzo-p-dioxin and directly interacting with target genes by binding to xenobiotic responsive elements. An anti-ARNT antibody was raised in rabbits against the bacterially expressed ARNT of amino acids 21-328 from the N-terminal. Using this antibody, besides ARNT itself, we detected at least one protein, 120 kDa, in the immunoprecipitate of anti-ARNT antibodies in HepG2 cells as well as in Hepa-1 cells. However, this protein is not present in the immunoprecipitate of the anti-AHR antisera nor in that of the preimmune sera of the rabbits used for the immunization.