abbr. for aryl hydrocarbon receptor; a protein, encoded by the
Ah gene, that binds a number of aryl hydrocarbons and mediates their biochemical and toxic effects. It is activated when it binds a ligand, and then translocates from the cytoplasm to the nucleus, where it is believed to enhance gene transcription by binding to the
xenobiotic-response element sequence. It contains a basic helix-turn-helix motif; the DNA-binding form is a heterodimer of this protein and
ARNT.