Endoribonuclease ToxN

UniProtKB accession:  B8X8Z0

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UniProtKB description:  Toxic component of a type III toxin-antitoxin (TA) system. An endoribonuclease which is active independently of the ribosome, cleaving between the second and third A of AAA(U/G) sequences, although not all occurrences of this tetranucleotide are cleaved (PubMed:23267117). Digests many mRNA species, including its own transcript and its cognate antitoxin RNA ToxI. ToxI has 5.5 nearly identical 36 nucleotide-long repeats (a single repeat neutralizes the toxin in vivo); a single repeat folds into a pseudoknot which binds the toxin (PubMed:21240270). The ToxI precursor RNA is a preferential target in vivo and is progressively degraded to single repeat lengths as ToxN-ToxI complex self-assembly occurs (PubMed:23267117). In vivo expression of ToxI antitoxin inhibits endonuclease activity of ToxN (PubMed:23267117). The toxin alone inhibits growth when expressed in E.coli without causing cell lysis; this bacteriostatic effect is neutralized by cognate RNA antitoxin ToxI (PubMed:19124776, PubMed:23267117). Non-cognate antitoxin RNA from B.thuringiensis does not inhibit this toxin (PubMed:23267117). The RNA antitoxin is less stable than the proteinaceous toxin; synthesis of ToxI in the absence of new ToxN synthesis restores growth and also detectable accumulation of the ToxN protein (PubMed:19124776). Negatively regulates its own operon in complex with ToxI (PubMed:19633081). The toxin-antitoxin system functions in plasmid maintenance (a plasmid addiction system) (PubMed:23267117).