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 recomb inant Escherichia coli cultures harboring CI857-repressed lambda-based expr ession vectors. This event, that becomes evident about 30-40 min after the heat shock, takes place when using the lambda promoter system in Ind(-) lys ogenic strains, but not in others commonly employed for recombinant gene ex pression. These results strongly suggest that the thermosensitive CI857 rep ressor, encoded by the expression vector, competes with CI Ind(-) molecules for binding to the prophage operator region, allowing for expression of ly tic 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 expressi on systems based on p(L)/p(R)-CI857 in bacterial strains modified through l ambda Ind- gene transfer vehicles. (C) 1999 Federation of European Microbio logical Societies. Published by Elsevier Science B.V. All rights reserved.