An antisense RNA controls synthesis of an SOS-induced toxin evolved from an antitoxin

Mol Microbiol. 2007 May;64(3):738-54. doi: 10.1111/j.1365-2958.2007.05688.x.


Only few small, regulatory RNAs encoded opposite another gene have been identified in bacteria. Here, we report the characterization of a locus where a small RNA (SymR) is encoded in cis to an SOS-induced gene whose product shows homology to the antitoxin MazE (SymE). Synthesis of the SymE protein is tightly repressed at multiple levels by the LexA repressor, the SymR RNA and the Lon protease. SymE co-purifies with ribosomes and overproduction of the protein leads to cell growth inhibition, decreased protein synthesis and increased RNA degradation. These properties are shared with several RNA endonuclease toxins of the toxin-antitoxin modules, and we show that the SymE protein represents evolution of a toxin from the AbrB fold, whose representatives are typically antitoxins. We suggest that SymE promotion of RNA cleavage may be important for the recycling of RNAs damaged under SOS-inducing conditions.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Sequence
  • Antitoxins / chemistry
  • Antitoxins / genetics*
  • Antitoxins / metabolism
  • Bacterial Toxins / genetics*
  • Bacterial Toxins / metabolism
  • Base Sequence
  • Blotting, Northern
  • Electrophoresis, Polyacrylamide Gel
  • Evolution, Molecular
  • Immunoblotting
  • Models, Molecular
  • Molecular Sequence Data
  • Mutation
  • Plasmids / genetics
  • Promoter Regions, Genetic / genetics
  • Protease La / metabolism
  • Protein Biosynthesis / genetics
  • Protein Conformation
  • Protein Folding
  • RNA, Antisense / genetics*
  • RNA, Messenger / genetics
  • RNA, Messenger / metabolism
  • Ribosomal Proteins / metabolism
  • SOS Response, Genetics / genetics*
  • Sequence Homology, Amino Acid
  • Sequence Homology, Nucleic Acid


  • Antitoxins
  • Bacterial Toxins
  • RNA, Antisense
  • RNA, Messenger
  • Ribosomal Proteins
  • Protease La