Disclosed is a method for determining whether a test protein is capable of interacting with a nuclear hormone receptor protein. The method involves: (a) providing a host cell which contains (i) a reporter gene operably linked to a protein binding site; (ii) a first fusion gene which expresses a first fusion protein, the first fusion protein including a nuclear hormone receptor protein covalently bonded to a binding moiety which is capable of specifically binding to the protein binding site; and (iii) a second fusion gene which expresses a second fusion protein, the second fusion protein including the test protein covalently bonded to a weak gene activating moiety; and (b) determining whether the test protein increases expression of the reporter gene as an indication of its ability to interact with the nuclear hormone receptor protein. Such an interaction may be hormone dependent, hormone independnet, or hormone sensitive. Also disclosed is purified DNA encoding thyroid hormone receptor-interacting proteins and the polypeptides expressed from such DNA.