Cloning of genes for production of Escherichia coli Shiga-like toxin type II.

Genes controlling production of Shiga-like toxin type II (SLT-II) in Escherichia coli were cloned from the SLT-II-converting bacteriophage 933W and compared with the Shiga-like toxin type I (SLT-I) genes previously isolated and described from phage 933J. Subcloning analysis identified a region within the 4.9-kilobase EcoRI fragment of phage 933W that was associated with SLT-II production. Experiments with E. coli minicells containing these subclones demonstrated that the 4.9-kilobase EcoRI fragment encodes the structural genes for SLT-II. These experiments additionally showed the genetic organization of the SLT-II genes to be the same as that of the SLT-I genes, with the coding sequence for the large A subunit adjacent to that for the smaller B subunit. The mobilities of the SLT-II subunits in sodium dodecyl sulfate-polyacrylamide gels were slightly greater than those determined for the SLT-I subunits. Although apparent processing of the SLT-I subunits was observed with polymyxin B treatment of the labeled minicells, no processing of the SLT-II subunits was detected. Southern blot hybridization studies suggested that the DNA fragment carrying the SLT-II structural genes shares approximately 50 to 60% homology with the DNA of the SLT-I structural genes.