LAUSR

Precise control of CRISPR-Cas9 would improve its safety and applicability. Controlled CRISPR inhibition is a promising approach but is complicated by separate inhibitor delivery, incomplete deactivation, and slow kinetics. To overcome these obstacles, we engineered photocleavable guide RNAs (pcRNAs) that endow Cas9 nucleases and base editors with a built-in mechanism for light-based deactivation. pcRNA enabled the fastest (<1 min) and most complete (<1% residual indels) approach for Cas9 deactivation. It also exhibited significantly enhanced specificity with wild-type Cas9. Time-resolved deactivation revealed that 12-36 h of Cas9 activity or 2-4 h of base editor activity was sufficient to achieve high editing efficiency. pcRNA is useful for studies of the cellular response to DNA damage by abolishing sustained cycles of damage and repair that would otherwise desynchronize response trajectories. Together, pcRNA expands the CRISPR toolbox for precision genome editing and studies of DNA damage and repair.