The RNA molecule CsrB binds to the global regulatory protein CsrA and antagonizes its activity in Escherichia coli.

Mu Ya Liu,Gaojun Gui,David P Giedroc,James F Preston,Ümit Yüksel,Tony Romeo,Lawrence Oakford,Bangdong Wei

doi:10.1074/jbc.272.28.17502

Abstract

The RNA-binding protein CsrA (carbon storage regulator) is a new kind of global regulator, which facilitates specific mRNA decay. A recombinant CsrA protein containing a metal-binding affinity tag (CsrA-H6) was purified to homogeneity and authenticated by N-terminal sequencing, matrix-assisted laser desorption/ionization time of flight mass spectrometry, and other studies. This protein was entirely contained within a globular complex of approximately 18 CsrA-H6 subunits and a single approximately 350-nucleotide RNA, CsrB. cDNA cloning and nucleotide sequencing revealed that the csrB gene is located downstream from syd in the 64-min region of the Escherichia coli K-12 genome and contains no open reading frames. The purified CsrA-CsrB ribonucleoprotein complex was active in regulating glg (glycogen biosynthesis) gene expression in vitro, as was the RNA-free form of the CsrA protein. Overexpression of csrB enhanced glycogen accumulation in E. coli, a stationary phase process that is repressed by CsrA. Thus, CsrB RNA is a second component of the Csr system, which binds to CsrA and antagonizes its effects on gene expression. A model for regulatory interactions in Csr is presented, which also explains previous observations on the homologous system in Erwinia carotovora. A highly repeated nucleotide sequence located within predicted stem-loops and other single-stranded regions of CsrB, CAGGA(U/A/C)G, is a plausible CsrA-binding element.

Highlights

IntroductionThe RNA-binding protein CsrA (carbon storage regulator) is a new kind of global regulator, which facilitates specific mRNA decay
The RNA-binding protein CsrA is a new kind of global regulator, which facilitates specific mRNA decay
During studies on the genetic regulation of glycogen biosynthesis in Escherichia coli, a metabolic pathway that is induced as cultures enter the stationary phase of growth, we identified a gene encoding a factor that effects potent negative regulation of glycogen biosynthesis, csrA or “carbon storage regulator” [1, 2]

Summary

Introduction

The RNA-binding protein CsrA (carbon storage regulator) is a new kind of global regulator, which facilitates specific mRNA decay. Recent experiments of Chatterjee et al [6] and Cui et al [7] document a key regulatory role for the csrA homolog of the pathogenic Erwinia species, rsmA (repressor of stationary phase metabolites), in the expression of several virulence factors of soft rot disease of higher plants, including pectinase, cellulase, and protease activities, and further suggest that it may modulate the production of the quorum-sensing metabolite N-(3-oxohexanoyl)-L-homoserine lactone Homologs of this metabolite are secreted by numerous Gram-negative bacteria, in which they serve to activate the expression of a wide variety of genes in response to cell density Evidence that the regulatory factor encoded by the aepH region is the CsrB RNA homolog of E. carotovora will be discussed

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Conclusion