Construction of a genetic toggle switch in Escherichia coli

Abstract

It has been proposed1 that gene-regulatory circuits with virtually any desired property can be constructed from networks of simple regulatory elements. These properties, which include multistabil- ity and oscillations, have been found in specialized gene circuits such as the bacteriophage l switch2 and the Cyanobacteria circadian oscillator3 . However, these behaviours have not been demonstrated in networks of non-specialized regulatory compo- nents. Here we present the construction of a genetic toggle switchÐa synthetic, bistable gene-regulatory networkÐin 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 mutually inhibitory network. It is ¯ipped between stable states using transient chemical or thermal induction and exhibits a nearly ideal switching threshold. As a practical device, the toggle switch forms a synthetic, addressable cellular memory unit and has implications for biotechnology, biocomputing and gene therapy.