Symbol SymR RNA type Antisense RNA SO {{{SO}}} | Rfam RF01809 Domain(s) E. coli | |
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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. It is a type I toxin-antitoxin system, and is under regulation by the antitoxin, SymR.
Contents
Discovery of the system
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. 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.
Mechanism of toxicity
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. 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).
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.