Roger S. Zou
CRISPR-Cas9 has catalyzed a biotechnological revolution through convenient and programmable genome editing. Cas9 itself, however, only performs the first step — site-directed induction of DNA damage. Completion of editing relies on the cell’s DNA repair machinery, which has been challenging to characterize due to the lack of control over DNA damage induction. In the laboratory of Taekjip Ha, we sought to tackle this problem by developing two systems for very fast light-mediated control over Cas9 activation and deactivation. First, we demonstrated Cas9 activation within seconds of light exposure, which allowed greatly improved kinetic measurements of DNA damage induction and repair. We discovered that Cas9-induced DNA damage could be detected within two minutes and repaired within 15 minutes, which is much faster than previously believed. Second, we demonstrated Cas9 deactivation within seconds of light exposure. Using this system, we discovered that only a few hours of CRISPR activity were sufficient for efficient genome editing. This system also greatly reduced editing at unintended “off-target” sites, which enhances the safety of genome editing. Together, my work in Dr. Ha’s lab opens the door for control of CRISPR-Cas9 as an effective method for studying genome editing and DNA repair.