The CRISPR–Cas9 system is widely studied for its role as a phage defence system and for gene editing applications, but its evolutionary origins are poorly understood. Here the authors use ancestral sequence reconstruction to determine the evolutionary history and ancient protein sequences of Streptococcus pyogenes Cas9 ancestors.
- Borja Alonso-Lerma
- Ylenia Jabalera
- Raul Perez-Jimenez
