PT  - JOURNAL ARTICLE
AU  - Yavuz S. Dagdas
AU  - Janice S. Chen
AU  - Samuel H. Sternberg
AU  - Jennifer A. Doudna
AU  - Ahmet Yildiz
TI  - A conformational checkpoint between DNA binding and cleavage by CRISPR-Cas9
AID  - 10.1101/122242
DP  - 2017 Jan 01
TA  - bioRxiv
PG  - 122242
4099  - http://biorxiv.org/content/early/2017/03/30/122242.short
4100  - http://biorxiv.org/content/early/2017/03/30/122242.full
AB  - The Cas9 endonuclease is widely utilized for genome engineering applications by programming its single-guide RNA and ongoing work is aimed at improving the accuracy and efficiency of DNA targeting. DNA cleavage of Cas9 is controlled by the conformational state of the HNH nuclease domain, but the mechanism that governs HNH activation at on-target DNA while reducing cleavage activity at off-target sites remains poorly understood. Using single-molecule FRET, we identified an intermediate state of S. pyogenes Cas9, representing a conformational checkpoint between DNA binding and cleavage. Upon DNA binding, the HNH domain transitions between multiple conformations before docking into its active state. HNH docking requires divalent cations, but not strand scission, and this docked conformation persists following DNA cleavage. Sequence mismatches between the DNA target and guide RNA prevent transitions from the checkpoint intermediate to the active conformation, providing selective avoidance of DNA cleavage at stably bound off-target sites.