title: Transcription of the Shiga-like toxin type II and Shiga-like toxin type II variant operons of Escherichia coli.
abstract: Shiga-like toxin type II (SLT-II) and Shiga-like toxin type II variant (SLT-IIv) are cytotoxins produced by certain strains of Escherichia coli. Nucleotide sequence analyses had revealed that the structural genes for the A subunit and B subunit of SLT-II or SLT-IIv are arranged in an operon. Primer extension and S1 nuclease protection analyses identified a promoter for the slt-II operon 118 bases upstream of the slt-IIA gene. The slt-IIv promoter was demonstrated to be identical to the slt-II promoter. The slt-II and slt-IIv promoters differed significantly from the previously characterized Shiga toxin (stx) and Shiga-like toxin type 1 (slt-I) promoters. The transcriptional efficiencies of the stx and slt-II promoters were compared in fusions to the chloramphenicol acetyltransferase gene, and constitutive expression of the slt-II promoter was found to be equivalent to derepressed expression of the stx promoter. In contrast to the stx and slt-I promoters, the slt-II and slt-IIv promoters did not contain sequences for binding of the Fur repressor protein, and SLT-II production was not determined by iron levels in the media in various E. coli strains with wild-type or mutant ferric uptake regulation (fur) alleles. Northern (RNA) blot analysis demonstrated a single mRNA transcript for the slt-II operon, and further analysis of the slt-II operon by primer extension did not reveal an independent promoter for the B subunit gene. A putative rho-independent transcription terminator was identified 274 bases downstream of slt-IIB. These data indicated that the slt-II and slt-IIv operons differ from the stx/slt-I operon in regulation of their transcription by iron. Whether these regulatory differences enable the type I and type II groups of Shiga-like toxins to perform different roles in the pathogenesis of infectious diseases remains to be established.
authors.affiliation: Department of Microbiology, Uniformed Services University of the Health Sciences, Bethesda, Maryland 20814-4799.
authors.forename: L M
authors.initials: LM
authors.lastname: Sung
authors.forename: M P
authors.initials: MP
authors.lastname: Jackson
authors.forename: A D
authors.initials: AD
authors.lastname: O'Brien
authors.forename: R K
authors.initials: RK
authors.lastname: Holmes
mesh_terms: D000818:Animals; D001427:Bacterial Toxins / Q000235:genetics* / Q000494:pharmacology; D001483:Base Sequence; D002470:Cell Survival / Q000187:drug effects; D004768:Enterotoxins / Q000235:genetics*; D004926:Escherichia coli / Q000235:genetics*; D006367:HeLa Cells / Q000166:cytology / Q000187:drug effects; D006801:Humans; D008969:Molecular Sequence Data; D015345:Oligonucleotide Probes; D009876:Operon; D010957:Plasmids; D011401:Promoter Regions, Genetic; D015183:Restriction Mapping; D022622:Shiga Toxin 1; D022641:Shiga Toxin 2; D013728:Terminator Regions, Genetic; D014158:Transcription, Genetic; D014709:Vero Cells
chemical_list: D001427:Bacterial Toxins; D004768:Enterotoxins; D015345:Oligonucleotide Probes; D022622:Shiga Toxin 1; D022641:Shiga Toxin 2