CsrA of Bacillus subtilis regulates translation initiation of the gene encoding the flagellin protein (hag) by blocking ribosome binding

Mol Microbiol. 2007 Jun;64(6):1605-20. doi: 10.1111/j.1365-2958.2007.05765.x.


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.

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • Bacillus subtilis / genetics
  • Bacillus subtilis / growth & development
  • Bacillus subtilis / metabolism*
  • Bacillus subtilis / physiology
  • Bacterial Proteins / genetics
  • Bacterial Proteins / metabolism
  • Base Sequence
  • Flagellin / genetics*
  • Flagellin / metabolism
  • Gene Expression Regulation, Bacterial*
  • Molecular Sequence Data
  • Protein Biosynthesis*
  • RNA-Binding Proteins / genetics
  • RNA-Binding Proteins / metabolism*
  • Repressor Proteins / genetics
  • Repressor Proteins / metabolism*
  • Ribosomes / metabolism*


  • Bacterial Proteins
  • RNA-Binding Proteins
  • Repressor Proteins
  • Flagellin