Patent ID: 7807417

Claim:
An isolated mammalian cell comprising a gene expression modulation system comprising: (a) a first gene expression cassette that is capable of being expressed in said mammalian cell comprising a polynucleotide sequence that encodes a first polypeptide comprising: (i) a DNA-binding domain that recognizes a response element associated with a gene whose expression is to be modulated; (ii) an ecdysone receptor ligand binding domain; (b) a second gene expression cassette that is capable of being expressed in said mammalian cell comprising a polynucleotide sequence that encodes a second polypeptide comprising: (i) a transactivation domain; and (ii) a retinoid X receptor ligand binding domain; wherein the transactivation domain is from a nuclear receptor other than an ecdysone receptor, a retinoid X receptor, or an ultraspiracle receptor, wherein the ligand binding domains from the first polypeptide and the second polypeptide are different and dimerize wherein at least one of the first polypeptide and the second polypeptide does not contain the A and B domains of the corresponding ecdysone receptor or retinoid X receptor, and wherein said gene expression modulation system is more sensitive to a diacylhydrazine ligand than to a steroid ligand when expressed in a mammalian cell.