The difference in one sentence
Cas9 and Cas12 are cousins. Cas9 needs a G-rich signal next to its target and cuts cleanly across both strands. Cas12 needs a T-rich signal, cuts at an angle leaving ragged ends, can process several guides from one strand of RNA, and — usefully for diagnostics but awkwardly inside cells — keeps chopping up loose DNA once it has found its target.
| Aspect | CRISPR-Cas9 | CRISPR-Cas12a |
|---|---|---|
| Sequence signal required | G-rich PAM (NGG), after the target | T-rich PAM (TTTV), before the target |
| Where it can aim | GC-rich regions favoured | AT-rich regions accessible |
| Cut shape | Blunt | Staggered, with overhangs |
| Multiple guides | Each needs its own transcript | Processes its own guide array |
| Collateral activity | None | Cuts loose single-stranded DNA once activated |
| Diagnostics | Limited use | The basis of DETECTR-class tests |
| Clinical use | Approved medicine | Cell therapy trials |
Sources
- Cell (Zetsche et al.) · 2015
Cpf1 is a single RNA-guided endonuclease of a class 2 CRISPR-Cas system ↗