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 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.