CRISPR-Cas9 gene editing complex. Computer illustration showing the molecular structure of the CRISPR-Cas9 gene editing complex from Streptococcus pyogenes. The CRISPR-Cas9 protein is used in genome engineering to cut DNA (deoxyribonucleic acid). It uses a guide RNA (ribonucleic acid) sequence to cut DNA at a complementary site. The Cas9 protein is represented by the green ribbon, and the atoms of DNA and single-guide RNA are represented by spheres: carbon (black), hydrogen (white), nitrogen (blue), oxygen (red), phosphorus (orange).