The eukaryotic way to defend and edit genomes by sRNA-targeted DNA deletion

Ann N Y Acad Sci. 2015 Apr:1341:106-14. doi: 10.1111/nyas.12636. Epub 2015 Jan 7.


While there is currently burgeoning interest in the application of the CRISPR/Cas (clustered regularly interspaced short palindromic repeats/CRISPR-associated genes) to genome editing, it is perhaps not widely appreciated that this is the second discovery of a small RNA (sRNA)-targeted DNA-deletion system. The first sRNA-targeted DNA-deletion system to be discovered, which we call IES/Ias (internal eliminated sequence/IES-associated genes) to contrast with CRISPR/Cas, is found in ciliates, and, like CRISPR/Cas, is thought to serve as a form of immune defense against invasive DNAs. The manner in which the ciliate IES/Ias system functions is distinct from that of the CRISPR/Cas system in archaea and bacteria, and arose independently through a synthesis of RNA interference-derived and DNA-specific molecular components. Despite the major differences between CRISPR/Cas and IES/Ias, both systems face similar conceptual challenges in targeting invasive DNAs. In this review, we focus on the discovery, effects, function, and evolutionary consequences of the IES/Ias system.

Keywords: CRISPR/Cas; DNA excision; IES/Ias; genome editing; sRNA; sRNA-targeted DNA deletion.

Publication types

  • Review

MeSH terms

  • Archaea / genetics
  • Bacteria / genetics
  • Clustered Regularly Interspaced Short Palindromic Repeats / genetics
  • DNA / genetics*
  • Eukaryota / genetics*
  • Evolution, Molecular
  • Genome / genetics*
  • Models, Genetic
  • RNA, Small Untranslated / genetics*
  • Sequence Deletion*


  • RNA, Small Untranslated
  • DNA