CRISPR-Cas9 gene editing complex. Illustration of the CRISPR-Cas9 gene editing complex. 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 surface is shown in blue. The guide RNA is orange, and the double strands of the DNA are blue, with the cut area in yellow. CRISPR (Clustered Regularly Interspersed Palindromic Repeats) is a bacterial adaptive immunity system.