An Escherichia coli host strain useful for efficient overproduction of cloned gene products with NaCl as the inducer.

Salt-induced overexpression of genes cloned downstream of the phage T7 phi10 promoter was demonstrated in an Escherichia coli strain (GJ1158) which carries a single chromosomally integrated copy of the gene for phage T7 RNA polymerase under transcriptional control of the cis-regulatory elements of the osmoresponsive proU operon. Plasmids that have been constructed to obtain overproduction of individual target gene products in strain BL21(DE3) (by addition of isopropyl-beta-D-thiogalactopyranoside as an inducer) can directly be transformed into GJ1158. The NaCl induction regimen was also shown to be associated with a decreased propensity for sequestration of overexpressed target proteins within insoluble inclusion bodies.