Heat-inactivation of plasmid-encoded CI857 repressor induces gene expression from Ind ^- lambda prophage in recombinant Escherichia coli

We have observed significant cell lysis upon temperature up-shift of recombinant Escherichia coli cultures harboring CI857-repressed lambda-based expression vectors. This event, that becomes evident about 30-40 min after the heat shock, takes place when using the lambda promoter system in Ind - lysogenic strains, but not in others commonly employed for recombinant gene expression. These results strongly suggest that the thermosensitive CI857 repressor, encoded by the expression vector, competes with CI Ind - molecules for binding to the prophage operator region, allowing for expression of lytic genes from the integrated Ind - viral genome upon temperature up-shift. Transcription of viral lytic genes does not include unspecific expression of a reporter sulA::lacZ gene fusion carried in the prophage genome. These results prompt, however, to carefully evaluate the limitations of expression systems based on p(L)/p(R)-CI857 in bacterial strains modified through lambda Ind - gene transfer vehicles. Copyright (C) 1999 Federation of European Microbiological Societies.