The invention provides chimeric proteins having at least two
functional protein units, each containing the dimerization domain of a member of the
steroid /
thyroid hormone nuclear receptor superfamily. The chimeric proteins can fold under
crystallization conditions to form functional entities. The functional entities optionally contain a novel flexible
peptide linker of variable lengths between at least two of the
protein units. In a preferred embodiment, the
linker is designed to be increased in increments of 12 amino acids each to aid in preparation of variant chimeric proteins. The
DNA binding characteristics of the invention functional entities differ from those of wild-type complexes formed between “monomeric” receptors and their binding partners. Some functional entities, e.g. dimers expressed as fusion proteins, transactivate responsive promoters in a manner similar to wild-type complexes, while others do not promote
transactivation and function instead essentially as constitutive repressors. The invention further provides
nucleotide sequences encoding the invention chimeric proteins, cells containing such
nucleotide sequences, and methods for using the invention chimeric proteins to modulate expression of one or more exogenous genes in a subject
organism. In addition, isolated
protein crystals suitable for x-
ray diffraction analysis and methods for obtaining putative ligands for the invention chimeric proteins are provided.