Construction of a genetic toggle switch in Escherichia coli

It has been proposed(1) that gene-regulatory circuits with virtually any de sired property can be constructed from networks of simple regulatory elemen ts. These properties, which include multistability and oscillations, have b een found in specialized gene circuits such as the bacteriophage lambda swi tch(2) and the Cyanobacteria circadian oscillator(3), However, these behavi ours have not been demonstrated in networks of non-specialized regulatory c omponents. Here we present the construction of a genetic toggle switch-a sy nthetic, bistable gene-regulatory network-in Escherichia coli and provide a simple theory that predicts the conditions necessary for bistability, The toggle is constructed from any two repressible promoters arranged in a mutu ally inhibitory network. It is flipped between stable states using transien t chemical or thermal induction and exhibits a nearly ideal switching thres hold. As a practical device, the toggle switch forms a synthetic, addressab le cellular memory unit and has implications for biotechnology, biocomputin g and gene therapy.