<i>P</i>_<i>at</i> promoter sequence and activity.

<p>(<b>A</b>) Nucleotide sequence of the <i>p</i>_<i>at</i> region. The transcription start site mapped by primer extension is marked by a vertical arrow. -10 and -35 promoter motifs are underlined and the <i>axe</i> start codon is in bold. Palindromes potentially recognised by Axe-Txe are denoted by inverted horizontal arrows. (<b>B</b>) Primer extension analysis of <i>axe-txe</i> module. Total RNA from <i>E. coli</i> SC301467 cells harbouring a plasmid possessing the <i>axe-txe</i> operon was subjected to primer extension analysis (E) using a radioactively labelled primer that anneals within flanking vector sequences. Reactions were performed and analysed as outlined in Materials and Methods, and electrophoresed on a denaturing 6% polyacrylamide gel in parallel with nucleotide sequencing reactions (A, C, G, T) carried out with the same primer. The major product from the primer extension is marked as +1. (<b>C</b>) Autoregulation of <i>axe-txe</i> expression by Axe and Axe-Txe <i>in cis</i>. Transcriptional fusions of different fragments of the <i>axe-txe</i> operon to the <i>luxCDABE</i> operon in pBBRlux-amp plasmid were transformed into <i>E. coli</i> SC301467. Luminescence in RLU (relative luminescence units) was measured when cells obtained OD₆₀₀ ~0.4. The results are averages of at least three independent experiments.