Expression of IroN, the salmochelin siderophore receptor, requires mRNA activation by RyhB small RNA homologues

Roberto Balbontín, Nicolás Villagra, Maria Pardos de la Gándara, Guido Mora, Nara Figueroa-Bossi, Lionello Bossi

Research output: Contribution to journalArticlepeer-review

17 Citations (Scopus)

Abstract

The iroN gene of Salmonella enterica and uropathogenic Escherichia coli encodes the outer membrane receptor of Fe3+-bound salmochelin, a siderophore tailored to evade capture by the host's immune system. The iroN gene is under negative control of the Fur repressor and transcribed under iron limiting conditions. We show here that transcriptional de-repression is not sufficient to allow iroN expression, as this also requires activation by either of two partially homologous small RNAs (sRNAs), RyhB1 and RyhB2. The two sRNAs target the same sequence segment approximately in the middle of the 94-nucleotide 5′ untranslated region (UTR) of iroN mRNA. Several lines of evidence suggest that base pair interaction stimulates iroN mRNA translation. Activation does not result from the disruption of a secondary structure masking the ribosome binding site; rather it involves sequences at the 5′ end of iroN 5′ UTR. In vitro 'toeprint' assays revealed that this upstream site binds the 30S ribosomal subunit provided that RyhB1 is paired with the mRNA. Altogether, our data suggest that RyhB1, and to lesser extent RyhB2, activate iroN mRNA translation by promoting entry of the ribosome at an upstream 'standby' site. These findings add yet an additional nuance to the polychromatic landscape of sRNA-mediated regulation.

Original languageEnglish
Pages (from-to)139-155
Number of pages17
JournalMolecular Microbiology
Volume100
Issue number1
DOIs
Publication statusPublished - 1 Apr 2016

ASJC Scopus subject areas

  • Microbiology
  • Molecular Biology

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