Cas9 is an RNA-guided endonuclease that is naturally expressed by Streptococcus pyogenes. Catalytically active ribonucleoprotein (RNP) complexes are produced by incubating Cas9 with a sequence specific CRISPR RNA (crRNA) and a trans-activating crRNA (tracrRNA), which together activate the endonuclease and guide it to the ~20-nucleotide protospacer sequence in target dsDNA. Alternatively, Cas9 can be complexed with a synthetic guide RNA (sgRNA) that encodes both the crRNA and tracrRNA in a single RNA strand.

Recombinant Cas9 includes a C-terminal nuclear localization signal (NLS) derived from the human nucleoplasm in gene to allow for import of RNP complexes into the nucleus of transfected mammalian cells. RNP complexes can be used for in vitro cleavage assays using the included reaction buffer or transfected into competent cells using electroporation. Properly targeted Cas9 RNPs will specifically cleave dsDNA within the target sequence and remain bound to the target strand until denaturation or proteolytic digestion of the enzyme.

Cas9 storage buffer: 10 mM Tris-HCl, 300 mM NaCl, 1 mM TCEP, 0.1 mM EDTA, 50% Glycerol, pH 7.4 @ 25 °C.