Comprehensive alanine-scanning mutagenesis of Escherichia coli CsrA defines two subdomains of critical functional importance

Jeffrey Mercante, Kazushi Suzuki, Xiaodong Cheng, Paul Babitzke, Tony Romeo

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The RNA-binding protein CsrA (carbon storage regulator) of Escherichia coli is a global regulator of gene expression and is representative of the CsrA/RsmA family of bacterial proteins. These proteins act by regulating mRNA translation and stability and are antagonized by binding to small noncoding RNAs. Although the RNA target sequence and structure for CsrA binding have been well defined, little information exists concerning the protein requirements for RNA recognition. The three-dimensional structures of three CsrA/RsmA proteins were recently solved, revealing a novel protein fold consisting of two interdigitated monomers. Here, we performed comprehensive alanine-scanning mutagenesis on csrA of E. coli and tested the 58 resulting mutants for regulation of glycogen accumulation, motility, and biofilm formation. Quantitative effects of these mutations on expression of glgCA'-'lacZ, flhDC'-'lacZ, and pgaA'-'lacZ translational fusions were also examined, and eight of the mutant proteins were purified and tested for RNA binding. These studies identified two regions of the amino acid sequence that were critical for regulation and RNA binding, located within the first (β1, residues 2-7) and containing the last (β5, residues 40-47) β-strands of CsrA. The β1 and β5 strands of opposite monomers lie adjacent and parallel to each other in the three-dimensional structure of this protein. Given the symmetry of the CsrA dimer, these findings imply that two distinct RNA binding surfaces or functional subdomains lie on opposite sides of the protein.

Original languageEnglish (US)
Pages (from-to)31832-31842
Number of pages11
JournalJournal of Biological Chemistry
Issue number42
StatePublished - Oct 20 2006

All Science Journal Classification (ASJC) codes

  • Biochemistry
  • Molecular Biology
  • Cell Biology


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