Novel Mechanism of Escherichia coli Porin Regulation

Abstract

A novel mechanism of Escherichia coli porin regulation was discovered from multicopy suppressors that permitted growth of cells expressing a mutant OmpC protein in the absence of DegP. Analyses of two suppressors showed that both substantially lowered OmpC expression. Suppression activities were confined to a short DNA sequence, which we designated ipeX for inhibition of porin expression, and to DNA containing a 3-truncated ompR gene. The major effect of ipeX on ompC expression was exerted posttranscriptionally, whereas the truncated OmpR protein reduced ompC transcription. ipeX was localized within an untranslated region of 247 base pairs between the stop codon of nmpC-a remnant porin gene from the cryptic phage qsr (DLP12) genome-and its predicted Rho-independent transcriptional terminator. Interestingly, another prophage, PA-2, which encodes a porin similar to NmpC, known as Lc, has sequences downstream from lc identical to that of ipeX. PA-2 lysogenization leads to Lc expression and OmpC inhibition. Our data show that the synthesis of the lc transcript, whose 3 end contains the corresponding ipeX sequence, inhibits OmpC expression. Overexpression of ipeX RNA inhibited both OmpC and OmpF expression but not that of OmpA. ompC-phoA chimeric gene constructs revealed a 248-bp untranslated region of ompC required for ipeX-mediated inhibition. However, no sequence complementarity was found between ipeX and this region of ompC, indicating that inhibition may not involve simple base pairing between the two RNA molecules. The effect of ipeX on ompC, but not on ompF, was independent of the RNA chaperone Hfq.

Analysis of the Regulated Transcriptome of Neisseria meningitidis in Human Blood Using a Tiling Array

“…In fact, some sRNAs that could potentially regulate genes involved in bacterial metabolism (such as Bns1 for the methylcitrate synthesis pathway) and transport and binding (such as Bns4 for the regulation of the tonB gene) were significantly regulated during incubation in human blood. Moreover, we identified an sRNA, Bns3, transcribed from a prophage DNA element that can potentially regulate bacterial genes, as was already described for the sprD sRNA of S. aureus (6) and dicF (4) and ipeX (5) of E. coli and that might support the idea of the involvement of bacteriophages in bacterial pathogenesis (3,63).…”

Solute Transport Proteins and the Outer Membrane Protein NmpC Contribute to Heat Resistance of Escherichia coli AW1.7

“…In most strains of E. coli, nmpC is not expressed, as it contains an IS5 insertion near the 3Ј end of the coding region. In E. coli K-12, nmpC is located on the defective qsrЈ prophage and can be activated by the loss of the IS5B insertion element (12,23). The major porins normally present in E. coli are OmpC and OmpF (12).…”

Adaptive and Mutational Resistance: Role of Porins and Efflux Pumps in Drug Resistance

“…The expression of OmpX is enhanced upon exposure to different environmental stresses, including antibiotics like fluoroquinolones and novobiocin, salicylate, high-ionic-strength buffer, and the chelator dipyridyl (56). Additional studies indicated that the cascades that regulate porin expression in E. coli may be even more complex than this, involving numerous regulatory proteins and sRNAs, depending on the specific environmental signal involved (29).…”