CBP P300 FUNCTIONS AS A POSSIBLE TRANSCRIPTIONAL COACTIVATOR OF AH RECEPTOR NUCLEAR TRANSLOCATOR (ARNT)/

A heterodimer of AhR (aryl hydrocarbon receptor) and Arnt (AhR nuclear translocator) conveys a transactivation signal of aromatic hydrocarbo ns such as 2,3,7,8-tetrachloro dibenzo-p-dioxin and 3-methylcholanthre ne to the genes for a group of drug-metabolizing enzymes, This inducib le expression of the genes is inhibited by adenovirus E1A, suggesting that CBP/p300 is somehow involved in the transactivation of the genes by the AhR and Amt heterodimer. Yeast and mammalian two hybrid systems revealed that CBP/p300 interacted with the transactivation domain of Arnt, but not with that of AhR, via the CREB-binding domain, The pull down assay using GST-Arnt hybrid protein confirmed the interaction bet ween Arnt and CBP/p300, Considering these results and that Arnt or Arn t2 functions as a common partner in the formation of transcriptional r egulators with Other bHLH/PAS proteins such as AhR, HLF, and HIF-1 alp ha, the possibility arises that CBP/p300 is extensively involved as a coactivator in the transactivation process by bHLH/PAS (a conserved se quence motif among Per, Arnt, and Sim) heterodimer transcription facto rs through interaction with Amt or Arnt2.