Second-strand synthesis was carried out with 3′ to 5′ exo− Klenow Fragment (New England Biolabs Inc.). DNA was amplified using the Expand High Fidelity PLUS PCR system (Roche Diagnostics Corp.).

The team evaluated a variety of human cells and genes of interest and found that fusing DNA polymerase I or the Klenow fragment to the Cas9 enzyme minimized unforeseen large genomic DNA deletions ...