The HicAB cassette, a putative novel, RNA-targeting toxin-antitoxin system in archaea and bacteria

Bioinformatics. 2006 Nov 1;22(21):2581-4. doi: 10.1093/bioinformatics/btl418. Epub 2006 Aug 8.


Toxin-antitoxin systems (TAS) are abundant, diverse, horizontally mobile gene modules that encode powerful resistance mechanisms in prokaryotes. We use the comparative-genomic approach to predict a new TAS that consists of a two-gene cassette encoding uncharacterized HicA and HicB proteins. Numerous bacterial and archaeal genomes encode from one to eight HicAB modules which appear to be highly prone to horizontal gene transfer. The HicB protein (COG1598/COG4226) has a partially degraded RNAse H fold, whereas HicA (COG1724) contains a double-stranded RNA-binding domain. The stable combination of these two domains suggests a link to RNA metabolism, possibly, via an RNA interference-type mechanism. In most HicB proteins, the RNAse H-like domain is fused to a DNA-binding domain, either of the ribbon-helix-helix or of the helix-turn-helix class; in other TAS, proteins containing these DNA-binding domains function as antitoxins. Thus, the HicAB module is predicted to be a novel TAS whose mechanism involves RNA-binding and, possibly, cleavage.

Publication types

  • Research Support, N.I.H., Intramural

MeSH terms

  • Antitoxins
  • Archaea / genetics
  • Archaea / metabolism*
  • Bacteria / genetics
  • Bacteria / pathogenicity*
  • Bacterial Toxins / chemistry*
  • Bacterial Toxins / genetics
  • Bacterial Toxins / metabolism
  • Binding Sites
  • Gene Targeting
  • Integrons / genetics
  • Protein Binding
  • RNA, Archaeal / chemistry*
  • RNA, Archaeal / metabolism
  • RNA, Bacterial / chemistry*
  • RNA, Bacterial / metabolism
  • RNA-Binding Proteins / chemistry*
  • RNA-Binding Proteins / genetics
  • RNA-Binding Proteins / metabolism
  • Sequence Analysis, Protein


  • Antitoxins
  • Bacterial Toxins
  • RNA, Archaeal
  • RNA, Bacterial
  • RNA-Binding Proteins