(a) Detection of chemiluminescent Cas9 protein and fluorescent nuclease activity for wild type (wt), the D10A and H840A nickase mutants with one active site disrupted, and the nuclease D10A/H840A dead Cas9 (dCas9). (b) Detection of Cas9 protein and activity in human HEK293T cells transfected with on-target AAVS1 guide (AAVS1), off-target guide (scrambled), or an untransfected control. Error bars represent standard deviation, points are average of four replicates.