SymE-SymR toxin-antitoxin system

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SymR SScons.png
Conserved secondary structure of SymR RNA.
Other data
RNA typeAntisense RNA
Domain(s)E. coli
PDB structuresPDBe
SymE Toxin of Type I toxin-antitoxin system

The SymE-SymR toxin-antitoxin system consists of a small hydrophobic toxin named SymE and a non-coding RNA called SymR which inhibits its translation.[1] It is a type I toxin-antitoxin system, and is under regulation by the antitoxin, SymR.[2]

Discovery of the system[edit]

SymR was originally labelled RyjC and is a 77nt RNA with a σ70 promoter. RyjC was found to overlap the yjiW open reading frame on the opposite strand by 6nt, and was characterised as an antisense RNA which bound the 5' untranslated region of yjiW.[3] Further study led to the renaming of both yjiW and RyjC to SymE (SOS-induced yjiW gene with similarity to MazE) and SymR (symbiotic RNA) respectively.[1]

Mechanism of toxicity[edit]

SymR blocks translation of SymE by antisense binding. SymE exhibits its toxicity by repressing global translation within the cell, cleaving mRNA in a similar manner to MazF, another toxin.[4] Quantitative Northern blot experiments showed that SymR RNA is present in cells at 10 times the concentration of SymE mRNA (0.02 fmol μg−1 and 0.2 fmol μg−1).[1]

Following DNA damage, the SOS response represses transcription of SymR RNA, allowing SymE toxin to degrade potentially damaged mRNA until the DNA has been repaired.[1]

See also[edit]


  1. ^ a b c d Kawano M, Aravind L, Storz G (May 2007). "An antisense RNA controls synthesis of an SOS-induced toxin evolved from an antitoxin". Mol. Microbiol. 64 (3): 738–54. doi:10.1111/j.1365-2958.2007.05688.x. PMC 1891008. PMID 17462020.
  2. ^ Kawano, M (December 2012). "Divergently overlapping cis-encoded antisense RNA regulating toxin-antitoxin systems from E. coli: hok/sok, ldr/rdl, symE/symR". RNA Biology. 9: 1520–7. doi:10.4161/rna.22757. PMID 23131729.
  3. ^ Kawano M, Reynolds AA, Miranda-Rios J, Storz G (2005). "Detection of 5'- and 3'-UTR-derived small RNAs and cis-encoded antisense RNAs in Escherichia coli". Nucleic Acids Res. 33 (3): 1040–50. doi:10.1093/nar/gki256. PMC 549416. PMID 15718303. Retrieved 2010-08-26.
  4. ^ Gerdes K, Wagner EG (April 2007). "RNA antitoxins". Curr. Opin. Microbiol. 10 (2): 117–24. doi:10.1016/j.mib.2007.03.003. PMID 17376733. Retrieved 2010-08-26.

Further reading[edit]

External links[edit]