Cas9 Nuclease Nickase H840A, S. pyogenes (nCas9), is an RNA-guided endonuclease that catalyzes site specific nicking of a single strand of double stranded DNA. The location of the break is within the target sequence 3 bases from the NGG PAM (Protospacer Adjacent Motif). The PAM sequence, NGG, must follow the targeted region on the opposite strand of the DNA with respect to the region complementary sgRNA sequence.