Taekjip Ha from Johns Hopkins University is the Kavli colloquium speaker of Spring 2020. He has pioneered several single-molecule fluorescence techniques.

CRISPR and DNA repair

Double strand breaks (DSB) are frequently generated, and researchers have discovered many proteins and processes needed to repair the breaks. However, relative timing of sub-stages of DNA repair or even their ordering has been difficult to determine due to the lack of method to synchronize the generation of well-defined breaks in living cells. Exposing cells to X-ray and UV can produce massive DNA damages at a defined time point, but the nature of the damage is ill-defined, and damages are made randomly. CRISPR-Cas systems allow the generation of breaks at specifically defined genome locations, but despite many attempts to develop ligand- or light-inducible CRISPR-Cas systems, the cleavage kinetics remains slow, leading to unsynchronized repair. We developed a very fast CRISPR-Cas9 can generate a DNA break at a defined locus at a well-define (within seconds) time point, allowing us to reveal the mechanisms of break recognition and study DSB repair and other cellular processes with an unprecedented spatiotemporal control.