CRISPR-Cas9 gene editing complex, animated molecular structure. 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 shown as ribbons (green), while the guide RNA and the double-strand of the DNA are shown as helical molecules (pink, blue and orange). CRISPR stands for clustered regularly interspaced short palindromic repeats.