Proving that the field of RNA-guided nucleases for gene editing is only in its infancy, a novel non-Cas9 CRISPR system isolated from Francisella novicida strain U112 by Zetsche et al in September 2015.

The system works in a similar fashion to CRISPR-Cas9, with a nuclease being recruited to a target site by sequence homology, However it differs from Cas9 in that:

  • It prefers a TTN protospacer associated motif (PAM) that is located 5' to the cut site
  • It does not require a seperate transactivating CRISPR RNA (tracrRNA), meaning the RNA sequence required for genome editing is significantly shorter at about 43 nucleotides long (Cas9 by comparison needs about 100nt)
  • Cleavage by Cpf1 results in 'sticky ends' due to cut sites being staggered by about 5 bases.

The discovery of this system further expands the genome editors tool box - potentially making available target sites that, due to PAM constraints, would not be available to Cas9. Further to this the authors hypothesise that the nature of Cpf1 cuts, being both sticky and distal to the PAM site may have some added advantages for homology directed repair.

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