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A feed-forward loop between SroC and MgrR small RNAs modulates the expression of eptB and the susceptibility to polymyxin B in Salmonella Typhimurium
Small non-coding RNAs (sRNAs) are well known regulators of gene expression that most often modulates the translation and decay of multiple mRNA targets. However, a novel type of regulatory RNAs has become a focus of attention; the sponge RNAs that sequester sRNAs by direct base-pairing. Given the intrinsic properties of the Hfq-binding RNAs, we wanted to explore the possibility that the known RNA sponge SroC targets additional sRNAs. Our findings expand the knowledge about the sponge role of SroC in the control of gene expression and illustrate the raising complexity of the regulatory network related to Salmonella LPS.
- Authors: Lillian G. Acuña1,2 , M. José Barros1 , Diego Peñaloza1 , Paula I. Rodas3 , Daniel Paredes-Sabja4,5 , Juan A. Fuentes1 , Fernando Gil1 , Iván L. Calderón1
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- VIEW AFFILIATIONS
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1 1Laboratorio de Genética y Patogénesis Bacteriana, Facultad de Ciencias Biológicas, Universidad Andres Bello, Santiago, Chile 2 2Laboratorio de Ecofisiología Microbiana, Fundación Ciencia para la Vida, Santiago, Chile 3 3Center for Integrative Medicine and Innovative Sciences, Facultad de Medicina, Universidad Andres Bello, Santiago, Chile 4 4Departamento de Ciencias Biológicas, Microbiota-Host Interaction and Clostridia Research Group, Facultad de Ciencias Biológicas, Universidad Andres Bello, Santiago, Chile 5 5Center for Bioinformatics and Integrative Biology, Facultad de Ciencias Biológicas, Universidad Andres Bello, Santiago, Chile
- Correspondence Iván L. Calderón [email protected]
- First Published Online: 23 November 2016, Microbiology 162: 1996-2004, doi: 10.1099/mic.0.000365
- Subject: Regulation
- Received:
- Accepted:
- Cover date:




A feed-forward loop between SroC and MgrR small RNAs modulates the expression of eptB and the susceptibility to polymyxin B in Salmonella Typhimurium, Page 1 of 1
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Base-pairing small RNAs (sRNAs) regulate gene expression commonly by direct interaction with cognate mRNAs. Nevertheless, recent studies have expanded this knowledge with the discovery of the RNA ‘sponges’ which are able to interact and repress the functions of classical base-pairing sRNAs. In this work, we present evidence indicating that the sponge RNA SroC from Salmonella enterica serovar Typhimurium base pairs with the MgrR sRNA, thereby antagonizing its regulatory effects on both gene expression and resistance to the antimicrobial peptide polymyxin B (PMB). By a predictive algorithm, we determined putative SroC–MgrR base-pairing regions flanking the interaction area between MgrR and its target mRNA, eptB, encoding a LPS-modifying enzyme. With a two-plasmid system and compensatory mutations, we confirmed that SroC directly interacts and down-regulates the levels of MgrR, thus relieving the MgrR-mediated repression of eptB mRNA. Since it was previously shown that an Escherichia coli strain carrying an mgrR deletion is more resistant to PMB, we assessed the significance of SroC in the susceptibility of S. Typhimurium to PMB. Whereas the sroC deletion increased the sensitivity to PMB, as compared to the wild-type, the resistance phenotypes between the ΔmgrR and ΔsroCΔmgrR strains were comparable, evidencing that mgrR mutation is epistatic to the sroC mutation. Together, these results indicate that both SroC and MgrR sRNAs compose a coherent feed-forward loop controlling the eptB expression and hence the LPS modification in S. Typhimurium.
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Edited by: M. Whiteley
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Edited by: M A. Schembri
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One supplementary table and one supplementary figure are available with the online Supplementary Material.
- Keyword(s): MgrR, sRNAs, polymyxin B, RNA sponge, SroC
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Abbreviations: PMB polymyxin B qRT-PCR quantitative real-time PCR
© 2016 The Authors
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