TABLE 1.
Classification of the main CRISPR/Cas RNA‐targeting systems
| Effector | Class and type | Organism(S) harbouring respective types | Signature components | Protospacer requirements | References |
|---|---|---|---|---|---|
| RCas9 | Class 2, type II | Streptococcus pyogenes |
Cas9 PAMmer sgRNA |
5’‐NGG‐3′ | O'Connell et al. (2014) |
| FnCas9 | Class 2, type II | Francisella novicida |
Cas9 sgRNA |
5’‐NG‐3′ |
Price et al. (2015) Sampson et al. (2013) |
| Cas13a | Class 2, type VI‐A |
Leptotrichia shahii Leptotrichia wadei |
Cas13 crRNA |
3′‐A/U/C‐5′ (not required by all orthologues) |
Abudayyeh et al. (2016) Abudayyeh et al. (2017) |
| Cas13b | Class 2, type VI‐B |
Prevotella buccae Bergeyella zoohelcum |
Cas13 crRNA |
5′‐A/U/G and 3′‐NAN or NNA (not required by all orthologues) | Smargon et al. (2017) |
| Cas13d | Class 2, type VI‐D |
Ruminococcus flavefaciens Eubacterium siraeum |
CasRx crRNA |
– |
Konermann et al. (2018) Yan et al. (2018) |