title: The small RNA RyhB activates the translation of shiA mRNA encoding a permease of shikimate, a compound involved in siderophore synthesis.
abstract: RyhB is a small RNA (sRNA) that downregulates about 20 genes involved in iron metabolism. It is expressed under low iron conditions and pairs with specific mRNAs to trigger their rapid degradation by the RNA degradosome. In contrast to this, another study has suggested that RyhB also activates several genes by increasing their mRNA level. Among these activated genes is shiA, which encodes a permease of shikimate, an aromatic compound participating in the biosynthesis of siderophores. Here, we demonstrate in vivo and in vitro that RyhB directly pairs at the 5'-untranslated region (5'-UTR) of the shiA mRNA to disrupt an intrinsic inhibitory structure that sequesters the ribosome-binding site (Shine-Dalgarno) and the first translation codon. This is the first demonstration of direct gene activation by RyhB, which has been exclusively described in degradation of mRNAs. Our physiological results indicate that the transported compound of the ShiA permease, shikimate, is important under conditions of RyhB expression, that is, iron starvation. This is demonstrated by growth assays in which shikimate or the siderophore enterochelin correct the growth defect observed for a ryhB mutant in iron-limited media.
authors.affiliation: Département de Biochimie, Groupe ARN, Université de Sherbrooke, Sherbrooke, Québec, Canada.
authors.forename: Karine
authors.initials: K
authors.lastname: Prévost
authors.forename: Hubert
authors.initials: H
authors.lastname: Salvail
authors.forename: Guillaume
authors.initials: G
authors.lastname: Desnoyers
authors.forename: Jean-François
authors.initials: JF
authors.lastname: Jacques
authors.forename: Emilie
authors.initials: E
authors.lastname: Phaneuf
authors.forename: Eric
authors.initials: E
authors.lastname: Massé
mesh_terms: D020121:5' Untranslated Regions; D026901:Membrane Transport Proteins / Q000378:metabolism; D008954:Models, Biological; D014176:Protein Biosynthesis; D012329:RNA, Bacterial / Q000235:genetics / Q000378:metabolism*; D012333:RNA, Messenger / Q000378:metabolism*; D012765:Shikimic Acid / Q000378:metabolism*; D017262:Siderophores / Q000096:biosynthesis*
chemical_list: D020121:5' Untranslated Regions; D026901:Membrane Transport Proteins; D012329:RNA, Bacterial; D012333:RNA, Messenger; D017262:Siderophores; D012765:Shikimic Acid