Fig. 6.

Light strategies to regulate the activity of CRISPR/Cas9 system. a A photoactivatable CRISPR/Cas9 transcription system. Blue light illumination causes the formation of dCas9-CIB-CRY2-activator complex which can promote target gene transcription. b A photoactivatable split Cas9. Blue light illumination can promote the heterodimerization of the split Cas9 fragments via pMag-nMag interaction, leading to the restoration of Cas9 activity. c Cas9-RsLOV2 homodimer dissociates under blue light irradiation, allowing the release of Cas9-RsLOV2 monomer and getting rid of the steric inhibition effect, thus restoring the activity of Cas9. d With the illumination of 500 nm light, pdDronpa1 dimer will be dissociated, leading to the reactivation of Cas9 or dCas9 activity. e The insertion of photocaged lysine to a specific domain of the Cas9 protein can make Cas9 inactive, until the photocaged lysine is removed under the light irradiation. f The photocleavable ssDNA oligonucleotide termed as “protector” can bind to the sgRNA and block CRISPR activity until the protector oligonucleotides are photolyzed by UV irradiation