Patent ID: 7579326

Claim:
An inducible expression system comprising: (a) a first expression cassette including a promoter operably linked to a first nucleic acid sequence encoding a regulator protein, wherein the regulator protein comprises: a mutated GAL-4 DNA-binding domain that carries a mutation in a helical domain located in a region from amino acid 54-93 of SEQ ID NO: 10, wherein the mutation in the helical domain decreases dimerization of the regulator protein occurring in the absence of a anti-progestin ligand, a transregulatory domain selected from the group consisting of NFkappaBp65, VP-16, TAF-1, TAF-2, TAU-1, TAU-2, TEF-1 and ORF-10 transregulatory domains, and a ligand-binding domain of a progesterone receptor, wherein the ligand binding domain has a deletion in naturally occurring amino acids in a region encompassing from about 1 to about 60 carboxyl terminal amino acids of the ligand binding domain, said deletion conferring an ability to be activated by an anti-progestin ligand; and (b) a second expression cassette having a second nucleic acid sequence encoding a desired product, operably linked to a promoter comprising a GAL-4 binding site, wherein the regulator protein is activated in the presence of the anti-progestin and the expression of the second nucleic acid sequence is controlled by binding of the activated regulator protein to Gal-4 binding sites in the promoter region of the second expression cassette.