Host cells and methods using a repressor polypeptide and an inducible promoter for gene expression

A method for expressing a nucleotide sequence of interest comprising:

• (a) providing a genetically modified host cell comprising (i) a first nucleic acid comprising a nucleotide sequence of interest operatively linked to a promoter which is modified to comprise an EilR binding site, (ii) a second nucleic acid comprising a nucleotide sequence encoding a repressor polypeptide comprising an amino acid sequence comprising a biologically active fragment of EilR having at least 70% amino acid identity with SEQ ID NO:1 wherein expression of the nucleotide sequence of interest from the promoter is induced by the presence of a hydrophobic inducer in that when the repressor polypeptide is bound to the hydrophobic inducer, the repressor polypeptide does not bind to the EilR binding site, wherein the nucleotide sequence of interest is heterologous to EilR or the biologically active fragment thereof, wherein when the repressor polypeptide has an amino acid sequence consisting of SEQ ID NO:1, then the nucleotide sequence of interest does not encode a green fluorescence protein (GFP);
• (b) introducing a hydrophobic cation inducer to the genetically modified host cell;
• and
• (c) expressing the nucleotide sequence of interest, or culturing or growing the genetically modified host cell such that nucleotide sequence of interest is expressed, such that the nucleotide sequence of interest is expressed at a rate higher when the hydrophobic cation inducer is present than if the hydrophobic cation inducer is not present in the genetically modified host cell.