A versatile and highly repressible Escherichia coli expression system based on invertible promoters: expression of a gene encoding a toxic product.

A very flexible and tightly regulatable expression system has been constructed. It uses the principle of invertible promoters [Podhajska et al., Gene 40 (1985) 163-168]. Here, we describe the construction of a plasmid that provides the integrase, which causes promoter inversion in a tightly regulated fashion, as well as modified plasmids carrying the invertible module. The way the integrase is provided on a separate plasmid closely mimicks expression of the integrase from a lambda lysogen. Thus, the flexibility of the original system is considerably extended by making it strain-independent without compromising the tight regulation. We present the expression of a single-chain T-cell receptor fragment as an example of application, in order to illustrate the properties of this expression system.