Patent ID: 7455988

Claim:
A method of inducing expression of a nucleotide sequence of interest in a eukaryotic cell, comprising: (a) providing a eukaryotic cell comprising (i) a promoter operably linked to the nucleotide sequence of interest; (ii) an operator downstream of the promoter, wherein the operator is a recognition site for a mutated restriction enzyme capable of binding but not cleaving DNA; and (iii) a nucleotide sequence encoding a regulatory fusion protein, wherein the fusion protein consists of (1) a transcription blocking domain that is a mutated restriction enzyme capable of binding but not cleaving DNA, and (2) a modified ligand-binding domain of a human estrogen receptor consisting of amino acids N304 to V595 of SEQ ID NO:8 and having amino acid modifications G400V, M543A, and L544A that allow tamoxifen binding, wherein the blocking domain binds the operator in the presence of a tamoxifen binding the ligand-binding domain and blocks expression of the nucleotide sequence of interest; (b) growing the cell of step (a) to a desired density in the presence of tamoxifen; and (c) removing tamoxifen from the presence of the cell, such that the expression of the nucleotide sequence of interest is induced.