| Summary: | Shiga-toxin producing <i>Escherichia coli</i> (STEC) causes human illness ranging from mild diarrhea to death. The bacteriophage encoded <i>stx</i> genes are located in the late transcription region, downstream of the antiterminator Q. The transcription of the <i>stx</i> genes is directly under the control of the late promoter <i>p</i>R’, thus the sequence diversity of the region between <i>Q</i> and <i>stx</i>, here termed the pR’ region, may affect Stx toxin production. Here, we compared the gene structure of the <i>p</i>R’ region and the <i>stx</i> subtypes of nineteen STECs. The sequence alignment and phylogenetic analysis suggested that the <i>p</i>R’ region tends to be more heterogeneous than the promoter itself, even if the prophages harbor the same <i>stx</i> subtype. Furthermore, we established and validated transcriptional fusions of the <i>p</i>R’ region to the DsRed reporter gene using mitomycin C (MMC) induction. Finally, these constructs were transformed into native and non-native strains and examined with flow cytometry. The results showed that induction levels changed when <i>p</i>R’ regions were placed under different regulatory systems. Moreover, not every <i>stx</i> gene could be induced in its native host bacteria. In addition to the functional genes, the diversity of the <i>p</i>R’ region plays an important role in determining the level of toxin induction.
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