Colicins are bacterial toxins that kill Escherichia coli and related cells; their mode of action is of interest in protein import and toxicology. Colicins translocate across the E. coli outer membrane and periplasm by interacting with several receptors. This translocation process involves interaction of the colicin with the outer membrane porin OmpF and subsequently with the integral membrane protein TolA. The N-terminal domain of colicin N is involved in the import process. Our aim was to produce a large quantity of colicin A for functional and structural studies. It is a prerequisite to have a correctly folded and stable protein for these studies. The commonly utilised expression system uses the Lex A promoter, which requires induction with toxic mitomycin C, though the yield is low. Here we present the production of an E. coli toxin and its immunity protein in E. coli using a safe inducible promoter.

Colicins are bacterial toxins that kill Escherichia coli and related cells; their mode of action is of interest in protein import and toxicology. Colicins translocate across the E. coli outer membrane and periplasm by interacting with several receptors. This translocation process involves interaction of the colicin with the outer membrane porin OmpF and subsequently with the integral membrane protein TolA. The N-terminal domain of colicin N is involved in the import process. Our aim was to produce a large quantity of colicin A for functional and structural studies. It is a prerequisite to have a correctly folded and stable protein for these studies. The commonly utilised expression system uses the Lex A promoter, which requires induction with toxic mitomycin C, though the yield is low. Here we present the production of an E. coli toxin and its immunity protein in E. coli using a safe inducible promoter.