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 a protein fragment ( 431 1158 ) from __SP__ __NODE__ protein is greater than binding of a protein fragment ( 431 1158 ) from __SP__ __NODE__ protein and a protein fragment containing a ligand binding domain from OR 1 [__NODE__] protein .