Identification of an ArgR-controlled promoter within the outermost region of the ISR mobile element.

Unlabelled: The transposon Tn is a prevalent composite element often detected in enteric bacteria, including those obtained from clinical samples. The Tn is flanked by two IS elements that work together in mediating transposition. IS-right (ISR) promotes transposition, while IS-left lacks a functional transposase and cannot transpose independently. ISR contains a weak promoter crucial for transposase transcription (pIN), along with two outward-oriented promoters, pOUT and OUTIIp, which may influence the expression of adjacent genes flanking the transposition site. Here, we report the identification of a novel outward-facing promoter, pOUT70, and a functional translation initiation region (TIR) within the last 70 nucleotides of ISR. Furthermore, we show that pOUT70 is negatively regulated by ArgR and positively controlled by IHF, and we demonstrate that pOUT70 enables growth phase-dependent expression of a truncated yet constitutively active version of the histidine kinase BarA. These findings underscore the significance of IS elements in enhancing downstream gene expression, and highlights the role of outward-facing promoters in derepressing virulence factors or acquiring antibiotic resistance.

Importance: Mobile genetic elements are small DNA fragments that can relocate within the genome, causing either gene inactivation or enhanced gene expression. Our research identified a new functional promoter and mRNA translation region within the IS10R element, which is part of the widely distributed transposon. We found that the global regulators ArgR and IHF control the activity of this promoter. Additionally, insertion of this mini- derivative into the gene resulted in the expression of a truncated but constitutive active form of the BarA sensor kinase. Overall, our work sheds light on how mobile genetic elements could impact the physiology and virulence of opportunistic pathogenic bacteria.