Figure 1. Inducible control of split Cas9.

(a) Schematic of the strategy for utilizing the ligand-binding domain of the oestrogen receptor, ERT (light green), to achieve tight control of CRISPR activity in split Cas9 (blue). The ERT-fused fragments of split Cas9 are segregated in the cytoplasm from the nuclear-localized sgRNA (green) through their interactions with Hsp90 (brown)²⁹,³⁰,³¹. Upon addition of 4-hydroxytamoxifen (4OHT, orange), the split fragments are released from Hsp90, and translocate into the nucleus to reconstitute an active split Cas9 complex. (b) Locations of split sites for the previously published split-1 (ref. ²⁴; beige) and three split candidates A (red), B (green) and C (blue) in the REC2 domain (yellow) of the Cas9 protein (grey) complexed with sgRNA (purple). PDB 4OO8 (ref. ³⁷).