Development of a Chromosomally Integrated Metabolite-Inducible Leu3p-α-IPM “Off-On” Gene Switch

BACKGROUND: Present technology uses mostly chimeric proteins as regulators and hormones or antibiotics as signals to induce spatial and temporal gene expression. METHODOLOGY/PRINCIPAL FINDINGS: Here, we show that a chromosomally integrated yeast ‘Leu3p-α-ΙΡΜ’ system constitutes a ligand-inducible regulatory “off-on” genetic switch with an extensively dynamic action area. We find that Leu3p acts as an active transcriptional repressor in the absence and as an activator in the presence of α-isopropylmalate (α-ΙΡΜ) in primary fibroblasts isolated from double transgenic mouse embryos bearing ubiquitously expressing Leu3p and a Leu3p regulated GFP reporter. In the absence of the branched amino acid biosynthetic pathway in animals, metabolically stable α-IPM presents an EC(50) equal to 0.8837 mM and fast “OFF-ON” kinetics (t(50)ON = 43 min, t(50)OFF = 2.18 h), it enters the cells via passive diffusion, while it is non-toxic to mammalian cells and to fertilized mouse eggs cultured ex vivo. CONCLUSIONS/SIGNIFICANCE: Our results demonstrate that the ‘Leu3p-α-ΙΡΜ’ constitutes a simpler and safer system for inducible gene expression in biomedical applications.