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.