Competition among Hfq-binding small RNAs in Escherichia coli

Mol Microbiol. 2011 Dec;82(6):1545-62. doi: 10.1111/j.1365-2958.2011.07907.x. Epub 2011 Nov 20.


A major class of small bacterial RNAs (sRNAs) regulate translation and mRNA stability by pairing with target mRNAs, dependent upon the RNA chaperone Hfq. Hfq, related to the Lsm/Sm families of splicing proteins, binds the sRNAs and stabilizes them in vivo and stimulates pairing with mRNAs in vitro. Although Hfq is abundant, the sRNAs, when induced, are similarly abundant. Therefore, Hfq may be limiting for sRNA function. We find that, when overexpressed, a number of sRNAs competed with endogenous sRNAs for binding to Hfq. This correlated with lower accumulation of the sRNAs (presumably a reflection of the loss of Hfq binding), and lower activity of the sRNAs in regulating gene expression. Hfq was limiting for both positive and negative regulation by the sRNAs. In addition, deletion of the gene for an expressed and particularly effective competitor sRNA improved the regulation of genes by other sRNAs, suggesting that Hfq is limiting during normal growth conditions. These results support the existence of a hierarchy of sRNA competition for Hfq, modulating the function of some sRNAs.

Publication types

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

MeSH terms

  • Escherichia coli / genetics
  • Escherichia coli / metabolism*
  • Escherichia coli Proteins / genetics
  • Escherichia coli Proteins / metabolism*
  • Gene Expression Regulation, Bacterial
  • Host Factor 1 Protein / genetics
  • Host Factor 1 Protein / metabolism*
  • Protein Binding
  • RNA, Bacterial / genetics
  • RNA, Bacterial / metabolism*
  • RNA, Small Untranslated / genetics
  • RNA, Small Untranslated / metabolism*


  • Escherichia coli Proteins
  • Hfq protein, E coli
  • Host Factor 1 Protein
  • RNA, Bacterial
  • RNA, Small Untranslated