The present invention relates to a method of screening compounds for binding to hsp90 by exposing a compound to hsp90 or a polypeptide fragment thereof containing amino acid residues 538-728 of the full length protein and determining whether the compound binds to hsp90 of the polypeptide fragment thereof. Also disclosed is a method of screening compounds for inhibition of hsp90 activity. The present invention further relates to a method of screening compounds as a cancer therapeutic and a method of treating cancerous conditions. Also disclosed is a method of inhibiting transcription-inducing activity of an aryl hydrocarbon receptor in a cell and a method of modifying expression of a gene that is activated by an aryl hydrocarbon receptor.
