TY - JOUR
T1 - Expression of IroN, the salmochelin siderophore receptor, requires mRNA activation by RyhB small RNA homologues
AU - Balbontín, Roberto
AU - Villagra, Nicolás
AU - Pardos de la Gándara, Maria
AU - Mora, Guido
AU - Figueroa-Bossi, Nara
AU - Bossi, Lionello
N1 - Publisher Copyright:
© 2016 John Wiley & Sons Ltd.
PY - 2016/4/1
Y1 - 2016/4/1
N2 - 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.
AB - 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.
UR - http://www.scopus.com/inward/record.url?scp=84961392965&partnerID=8YFLogxK
U2 - 10.1111/mmi.13307
DO - 10.1111/mmi.13307
M3 - Article
C2 - 26710935
AN - SCOPUS:84961392965
SN - 0950-382X
VL - 100
SP - 139
EP - 155
JO - Molecular Microbiology
JF - Molecular Microbiology
IS - 1
ER -