Snapshots of a tiny ancestral nuclease of Cas9

High-resolution structures solved by Schuler et al. shed light on how Cas9’s evolutionary ancestor IscB operates as an RNA-guided nuclease. With only two-fifths the size of Cas9, IscB holds great promise for alleviating the cargo size constraint of in vivo CRISPR delivery. High-resolution structures solved by Schuler et al. shed light on how Cas9’s evolutionary ancestor IscB operates as an RNA-guided nuclease. With only two-fifths the size of Cas9, IscB holds great promise for alleviating the cargo size constraint of in vivo CRISPR delivery.