title: CsrA of Bacillus subtilis regulates translation initiation of the gene encoding the flagellin protein (hag) by blocking ribosome binding.
abstract: The global regulatory Csr (carbon storage regulator) and the homologous Rsm (repressor of secondary metabolites) systems of Gram-negative bacteria typically consist of an RNA-binding protein (CsrA/RsmA) and at least one sRNA that functions as a CsrA antagonist. CsrA modulates gene expression post-transcriptionally by regulating translation initiation and/or mRNA stability of target transcripts. While Csr has been extensively studied in Gram-negative bacteria, until now Csr has not been characterized in any Gram-positive organism. csrA of Bacillus subtilis is the last gene of a flagellum biosynthetic operon. In addition to the previously identified sigma(D)-dependent promoter that controls expression of the entire operon, a sigma(A)-dependent promoter was identified that temporally controls expression of the last two genes of the operon (fliW-csrA); expression peaks 1 h after cell growth deviates from exponential phase. hag, the gene encoding flagellin, was identified as a CsrA-regulated gene. CsrA was found to repress hag'-'lacZ expression, while overexpression of csrA reduces cell motility. In vitro binding studies identified two CsrA binding sites in the hag leader transcript, one of which overlaps the hag Shine-Dalgarno sequence. Toeprint and cell-free translation studies demonstrate that bound CsrA prevents ribosome binding to the hag transcript, thereby inhibiting translation initiation and Hag synthesis.
authors.affiliation: Department of Biochemistry and Molecular Biology, The Pennsylvania State University, University Park, PA 16802, USA.
authors.forename: Helen
authors.initials: H
authors.lastname: Yakhnin
authors.forename: Pallavi
authors.initials: P
authors.lastname: Pandit
authors.forename: Tom J
authors.initials: TJ
authors.lastname: Petty
authors.forename: Carol S
authors.initials: CS
authors.lastname: Baker
authors.forename: Tony
authors.initials: T
authors.lastname: Romeo
authors.forename: Paul
authors.initials: P
authors.lastname: Babitzke
mesh_terms: D001412:Bacillus subtilis / Q000235:genetics / Q000254:growth & development / Q000378:metabolism* / Q000502:physiology; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism; D001483:Base Sequence; D005408:Flagellin / Q000235:genetics* / Q000378:metabolism; D015964:Gene Expression Regulation, Bacterial; D008969:Molecular Sequence Data; D014176:Protein Biosynthesis; D016601:RNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D012097:Repressor Proteins / Q000235:genetics / Q000378:metabolism*; D012270:Ribosomes / Q000378:metabolism*
chemical_list: D001426:Bacterial Proteins; D016601:RNA-Binding Proteins; D012097:Repressor Proteins; D005408:Flagellin