Small RNA-induced differential degradation of the polycistronic mRNA iscRSUA

EMBO J. 2009 Jun 3;28(11):1551-61. doi: 10.1038/emboj.2009.116. Epub 2009 Apr 30.


Most polycistronic genes are expressed in a single transcript, in which each cistron produces a fixed amount of protein. In this report, we show the first example of differential degradation of a polycistronic gene induced by a small regulatory RNA (sRNA). Our data show that the iron-responsive sRNA, RyhB, binds to the second cistron of the polycistronic mRNA, iscRSUA, which encodes the necessary machinery for biosynthesis of Fe-S clusters, and promotes the cleavage of the downstream iscSUA transcript. This cleavage gives rise to the remaining 5'-section of the transcript encoding IscR, a transcriptional regulator responsible for activation and repression of several genes depending on the cellular Fe-S level. Our data indicate that the iscR transcript is stable and that translation is active. The stability of the iscR transcript depends on a 111-nucleotide long non-translated RNA section located between iscR and iscS, which forms a strong repetitive extragenic palindromic secondary structure and may protect against ribonucleases degradation. This novel regulation shows how sRNAs and mRNA structures can work together to modulate the transcriptional response to a specific stress.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Escherichia coli / physiology
  • Escherichia coli Proteins / biosynthesis*
  • Gene Expression Regulation, Bacterial
  • Iron / metabolism*
  • Models, Biological
  • Models, Molecular
  • Nucleic Acid Conformation
  • RNA Stability*
  • RNA, Small Interfering / metabolism*
  • Sulfur / metabolism*
  • Transcription Factors / biosynthesis*


  • Escherichia coli Proteins
  • IscR protein, E coli
  • RNA, Small Interfering
  • Transcription Factors
  • Sulfur
  • Iron