Cloning and expression of heat-labile enterotoxin operon of an enterotoxigenic human Escherichia coli strain.

Plasmid pJY11 of the Escherichia coli H10407 strain was isolated and completely digested with restriction endonuclease PstI in order to isolate the heat-labile enterotoxin (LT) operon. The resulting fragments were then separated by electrophoresis on agarose gel, and the location of the LT region in pJY11 was determined by Southern hybridization. The LT region was found to be located on a 5.3 kb fragment of pJY11. This fragment was recovered and subsequently ligated to PstI-linearized pUC8 DNA. After transformation and selection, a clone that effectively expressed LT was obtained. Biological and immunological assays showed the LT synthesized by this clone to be biologically and immunologically identical to that synthesized by the parent E. coli strain H10407; the LT production level of this recombinant strain was 15 times greater.