title: Circuitry linking the Csr and stringent response global regulatory systems.
abstract: CsrA protein regulates important cellular processes by binding to target mRNAs and altering their translation and/or stability. In Escherichia coli, CsrA binds to sRNAs, CsrB and CsrC, which sequester CsrA and antagonize its activity. Here, mRNAs for relA, spoT and dksA of the stringent response system were found among 721 different transcripts that copurified with CsrA. Many of the transcripts that copurified with CsrA were previously determined to respond to ppGpp and/or DksA. We examined multiple regulatory interactions between the Csr and stringent response systems. Most importantly, DksA and ppGpp robustly activated csrB/C transcription (10-fold), while they modestly activated csrA expression. We propose that CsrA-mediated regulation is relieved during the stringent response. Gel shift assays confirmed high affinity binding of CsrA to relA mRNA leader and weaker interactions with dksA and spoT. Reporter fusions, qRT-PCR and immunoblotting showed that CsrA repressed relA expression, and (p)ppGpp accumulation during stringent response was enhanced in a csrA mutant. CsrA had modest to negligible effects on dksA and spoT expression. Transcription of dksA was negatively autoregulated via a feedback loop that tended to mask CsrA effects. We propose that the Csr system fine-tunes the stringent response and discuss biological implications of the composite circuitry.
authors.affiliation: Department of Microbiology and Immunology, Emory University School of Medicine, Atlanta, GA 30322, USA.
authors.forename: Adrianne N
authors.initials: AN
authors.lastname: Edwards
authors.forename: Laura M
authors.initials: LM
authors.lastname: Patterson-Fortin
authors.forename: Christopher A
authors.initials: CA
authors.lastname: Vakulskas
authors.forename: Jeffrey W
authors.initials: JW
authors.lastname: Mercante
authors.forename: Katarzyna
authors.initials: K
authors.lastname: Potrykus
authors.forename: Daniel
authors.initials: D
authors.lastname: Vinella
authors.forename: Martha I
authors.initials: MI
authors.lastname: Camacho
authors.forename: Joshua A
authors.initials: JA
authors.lastname: Fields
authors.forename: Stuart A
authors.initials: SA
authors.lastname: Thompson
authors.forename: Dimitris
authors.initials: D
authors.lastname: Georgellis
authors.forename: Michael
authors.initials: M
authors.lastname: Cashel
authors.forename: Paul
authors.initials: P
authors.lastname: Babitzke
authors.forename: Tony
authors.initials: T
authors.lastname: Romeo
mesh_terms: D001483:Base Sequence; D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism*; D029968:Escherichia coli Proteins / Q000235:genetics / Q000378:metabolism*; D015964:Gene Expression Regulation, Bacterial; D008969:Molecular Sequence Data; D011485:Protein Binding; D012329:RNA, Bacterial / Q000235:genetics / Q000378:metabolism*; D062085:RNA, Long Noncoding; D022661:RNA, Untranslated / Q000235:genetics / Q000378:metabolism*; D016601:RNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D012097:Repressor Proteins / Q000235:genetics / Q000378:metabolism*
chemical_list: C093587:CsrA protein, E coli; C107123:CsrB RNA, E coli; D029968:Escherichia coli Proteins; D012329:RNA, Bacterial; D062085:RNA, Long Noncoding; D022661:RNA, Untranslated; D016601:RNA-Binding Proteins; D012097:Repressor Proteins