Switchable Cas9

- Diverse Cas9 variants have been engineered that are switchable by external signals.
- Suitable signals include addition of small molecules, light and temperature changes.
- To achieve control, the Cas9 protein itself or its programmable RNAs are modified.
- Switchable Cas9 variants are engineered as split or single-chain proteins.
- Switchable variants mitigate effects caused by excessive and untimely Cas9 activity.

Ever since its discovery, Cas9 from Streptococcus pyogenes has revolutionized biology by enabling analysis and engineering of genomes with unprecedented precision and ease. To fine-tune on-target effects and to mitigate adverse effects caused by untimely and off-target action of Cas9, strategies have been developed to control its activity at the post-translational stage via external trigger signals. Control is either achieved by modifying the Cas9 protein itself or its programmable RNA molecules. To date, switchable Cas9 variants responding to small ligands, light or temperature have been engineered. With these variants in hand, the regulation and modification of genomes can be accomplished in graded and ever more precise manner.

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