title: An RpoS-dependent sRNA regulates the expression of a chaperone involved in protein folding.
abstract: Small noncoding RNAs (sRNAs) are usually expressed in the cell to face a variety of stresses. In this report we disclose the first target for SraL (also known as RyjA), a sRNA present in many bacteria, which is highly induced in stationary phase. We also demonstrate that this sRNA is directly transcribed by the major stress σ factor σ(S) (RpoS) in Salmonella enterica serovar Typhimurium. We show that SraL sRNA down-regulates the expression of the chaperone Trigger Factor (TF), encoded by the tig gene. TF is one of the three major chaperones that cooperate in the folding of the newly synthesized cytosolic proteins and is the only ribosome-associated chaperone known in bacteria. By use of bioinformatic tools and mutagenesis experiments, SraL was shown to directly interact with the 5' UTR of the tig mRNA a few nucleotides upstream of the Shine-Dalgarno region. Namely, point mutations in the sRNA (SraL*) abolished the repression of tig mRNA and could only down-regulate a tig transcript target with the respective compensatory mutations. We have also validated in vitro that SraL forms a stable duplex with the tig mRNA. This work constitutes the first report of a small RNA affecting protein folding. Taking into account that both SraL and TF are very well conserved in enterobacteria, this work will have important repercussions in the field.
authors.affiliation: Instituto de Tecnologia Química e Biológica, Universidade Nova de Lisboa, 2780-157 Oeiras, Portugal.
authors.forename: Inês Jesus
authors.initials: IJ
authors.lastname: Silva
authors.forename: Alvaro Darío
authors.initials: AD
authors.lastname: Ortega
authors.forename: Sandra Cristina
authors.initials: SC
authors.lastname: Viegas
authors.forename: Francisco
authors.initials: F
authors.lastname: García-Del Portillo
authors.forename: Cecília Maria
authors.initials: CM
authors.lastname: Arraiano
mesh_terms: D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D015964:Gene Expression Regulation, Bacterial; D018832:Molecular Chaperones / Q000235:genetics* / Q000378:metabolism; D017354:Point Mutation; D017510:Protein Folding; D012329:RNA, Bacterial / Q000235:genetics / Q000378:metabolism; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D058727:RNA, Small Untranslated / Q000235:genetics / Q000378:metabolism*; D012486:Salmonella typhimurium / Q000235:genetics / Q000378:metabolism; D012808:Sigma Factor / Q000235:genetics / Q000378:metabolism*
chemical_list: D001426:Bacterial Proteins; D018832:Molecular Chaperones; D012329:RNA, Bacterial; D012333:RNA, Messenger; D058727:RNA, Small Untranslated; D012808:Sigma Factor; C069567:sigma factor KatF protein, Bacteria
keywords: PPIase; RyjA; S. Typhimurium; SraL; σS
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