title: Expression of IroN, the salmochelin siderophore receptor, requires mRNA activation by RyhB small RNA homologues.
abstract: The iroN gene of Salmonella enterica and uropathogenic Escherichia coli encodes the outer membrane receptor of Fe(3+) -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.
authors.affiliation: Institute for Integrative Biology of the Cell (I2BC), CEA, CNRS, Université Paris-Sud, Université Paris-Saclay, 91198, Gif-sur-Yvette, France.
authors.forename: Roberto
authors.initials: R
authors.lastname: Balbontín
authors.affiliation: Laboratorio de Patogénesis Molecular y Antimicrobianos, Facultad de Medicina, Universidad Andres Bello, Echaurren 183, Santiago, Chile.
authors.forename: Nicolás
authors.initials: N
authors.lastname: Villagra
authors.affiliation: Institute for Integrative Biology of the Cell (I2BC), CEA, CNRS, Université Paris-Sud, Université Paris-Saclay, 91198, Gif-sur-Yvette, France.
authors.forename: Maria
authors.initials: M
authors.lastname: Pardos de la Gándara
authors.affiliation: Laboratorio de Patogénesis Molecular y Antimicrobianos, Facultad de Medicina, Universidad Andres Bello, Echaurren 183, Santiago, Chile.
authors.forename: Guido
authors.initials: G
authors.lastname: Mora
authors.affiliation: Institute for Integrative Biology of the Cell (I2BC), CEA, CNRS, Université Paris-Sud, Université Paris-Saclay, 91198, Gif-sur-Yvette, France.
authors.forename: Nara
authors.initials: N
authors.lastname: Figueroa-Bossi
authors.affiliation: Institute for Integrative Biology of the Cell (I2BC), CEA, CNRS, Université Paris-Sud, Université Paris-Saclay, 91198, Gif-sur-Yvette, France.
authors.forename: Lionello
authors.initials: L
authors.lastname: Bossi
mesh_terms: D020121:5' Untranslated Regions; D001425:Bacterial Outer Membrane Proteins / Q000235:genetics*; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism; D001483:Base Sequence; D001665:Binding Sites; D018387:Codon, Initiator; D017124:Conserved Sequence; D015964:Gene Expression Regulation, Bacterial; D009690:Nucleic Acid Conformation; D059372:Nucleotide Motifs; D011485:Protein Binding; D020871:RNA Stability; D012329:RNA, Bacterial / Q000737:chemistry / Q000235:genetics; D012333:RNA, Messenger / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D016601:RNA-Binding Proteins / Q000235:genetics / Q000378:metabolism; D011956:Receptors, Cell Surface / Q000235:genetics*; D012270:Ribosomes / Q000378:metabolism
chemical_list: D020121:5' Untranslated Regions; D001425:Bacterial Outer Membrane Proteins; D001426:Bacterial Proteins; D018387:Codon, Initiator; D012329:RNA, Bacterial; D012333:RNA, Messenger; D016601:RNA-Binding Proteins; D011956:Receptors, Cell Surface; C035902:siderophore receptors