Cloning and nucleotide sequencing of Vero toxin 2 variant genes from Escherichia coli O91:H21 isolated from a patient with the hemolytic uremic syndrome

Microb Pathog. 1990 Jan;8(1):47-60. doi: 10.1016/0882-4010(90)90007-d.


Cellular DNA extracted from Escherichia coli strain B2F1 (O91:H21) was found to contain two separate DNA sequences that hybridized with a Vero toxin 2 (VT2)-specific gene probe under stringent conditions. These two sequences were cloned and both were shown to encode a variant of Vero toxin 2 (VT2vh). The nucleotide sequences of the operons encoding VT2vh, designated as vtx2ha and vtx2hb, were determined. The two operons were nearly identical (99% overall DNA homology) and both encoded A subunits of 319 amino acid residues and B subunits of 89 amino acid residues, the A and B subunit genes being separated by a stretch of 14 bp. The A and B subunit genes of the vtx2ha operon exhibited 98.6% and 95.5% DNA homology, respectively, with those of the slt-II operon encoding Shiga-like toxin II (or VT2) cloned from a strain from a patient with hemorrhagic colitis, while the A and B subunit genes of the vtx2ha operon showed 94.5% and 82.8% DNA homology, respectively, with those of the slt-IIv operon encoding a SLT-II variant cloned from a strain isolated from a pig with edema disease. The nucleotide sequences of the presumed promoters and presumptive ribosome binding sites in the vtx2ha, vtx2hb, and slt-II, and slt-IIv operons were identical. These results indicate that nucleotide sequences encoding a family of VT2-related toxins are present in various strains of E. coli and that the sequences of the genes for A subunits are better conserved than those of the B subunit genes.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Sequence
  • Bacterial Toxins / genetics*
  • Base Sequence
  • Blotting, Southern
  • Cloning, Molecular
  • Escherichia coli / genetics*
  • Escherichia coli / isolation & purification
  • Genes, Bacterial
  • Hemolytic-Uremic Syndrome / microbiology*
  • Humans
  • Molecular Sequence Data
  • Operon
  • Restriction Mapping
  • Sequence Homology, Nucleic Acid
  • Shiga Toxin 1
  • Shiga Toxin 2


  • Bacterial Toxins
  • Shiga Toxin 1
  • Shiga Toxin 2