General features and properties of insertion sequence elements

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The casposases

More recently, TE related to CRISPRs, Casposons have been identified (Krupovic et al., 2014) and a reassement of their ends has led to the identification of an 14-15 bp target duplication (Hickman & Dyda, 2014). Moreover, the purified Cas1 enzyme encoded by these ancestral transposons has been demonstrated to catalyse strand transfer of a pre-cleaved transposon in vitro but does not appear to promote transposon strand cleavage in this assay (Hickman & Dyda, 2015). Cas1 "casposases" use similar chemistry to that used by the CRISPR Cas1-Cas2 complex but with opposite substrate specificities since CRISPR Cas1-Cas2 integrates "random" sequences into a specific site in the CRISPR locus whereas casposases integrate specific site (the casposon ends) into random target sequences.

    References :
  • Hickman AB & Dyda F (2014) CRISPR-Cas immunity and mobile DNA: a new superfamily of DNA transposons encoding a Cas1 endonuclease. Mob DNA 5: 23.
  • Hickman AB & Dyda F (2015) The casposon-encoded Cas1 protein from Aciduliprofundum boonei is a DNA integrase that generates target site duplications. Nucleic Acids Res 43: 10576-10587.
  • Krupovic M, Makarova KS, Forterre P, Prangishvili D & Koonin EV (2014) Casposons: a new superfamily of self-synthesizing DNA transposons at the origin of prokaryotic CRISPR-Cas immunity. BMC Biol 12: 36.