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Discovery of a novel immunity system against diverse bacterial nucleic acid degrading toxins

Wednesday, October 26, 2011 — Poster Session IV

2:00 p.m. – 4:00 p.m.

Natcher Conference Center




  • D Zhang
  • L Iyer
  • L Aravind


We characterize a novel superfamily (the SUKH superfamily) that unites a diverse group of proteins including Smi1/Knr4, PGs2, Fbxo3, Skip16, Syd, herpesviral US22, IRS1 and TRS1, and their bacterial homologs. Using contextual analysis we present evidence that its bacterial members are potential immunity proteins for a variety of toxin systems that also include the recently characterized contact-dependent inhibition (CDI) systems of proteobacteria. The associated toxins possess domains belonging to diverse nuclease and nucleic acid deaminase families, including at least eight distinct types of DNases of HNH/EndoVII- and restriction endonuclease-fold, and RNases of the EndoU-like and colicin E3-like cytotoxic RNases-folds. By using diverse N-terminal domains, these toxins are extruded by several distinct secretory mechanisms such as the two-partner system in proteobacteria, ESAT-6/WXG-like ATP-dependent secretory systems in Gram-positive bacteria and the conventional Sec-dependent system in several bacterial lineages. Unlike classical colicin-like nuclease toxins, the overwhelming majority of SUKH associated toxin systems is chromosomally encoded and appears to have diversified through a recombination process combining different C-terminal nuclease domains to N-terminal secretion-related domains. Across the bacterial superkingdom these systems might participate in discriminating "self" or kin from "non-self" or non-kin strains.

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