In cell free system , binding of heterodimer consisting of protein fragment ( 203 467 ) containing a ligand binding domain from __SP__ __NODE__ protein and of protein fragment containing a ligand binding domain from OR 1 [__NODE__] protein and __NODE__ 1 [__NODE__] protein is greater than binding of __NODE__ 1 [__NODE__] protein and a protein fragment ( 203 467 ) containing a ligand binding domain from __SP__ __NODE__ protein .