EnGen® Spy dCas9 is an inactive mutant of Cas9 nuclease that retains programmable DNA binding activity (1,2). EnGen Spy dCas9 contains two point mutations, D10A and H840A, which inactivate its RuvC and HNH nuclease domains, respectively. The N-terminal SNAP-tag® allows for covalent attachment of fluorophores, biotin, and a number of other conjugates useful for visualization and target enrichment. Like with Cas9 nuclease, DNA binding by EnGen Spy dCas9 requires a guide RNA complementary to a target sequence with a protospacer adjacent motif (PAM), NGG, downstream of the target sequence. EnGen Spy dCas9 contains a SV40 T antigen nuclear localization sequence (NLS) at the C- terminus of the protein.