CRISPR-CAS9 gene editing complex. Computer illustration showing the molecular structure of the CRISPR-associated protein Cas9 in complex with RNA (ribonucleic acid) and DNA (deoxyribonucleic acid, orange). Cas9 is a nuclease protein associated with the CRISPR (Clustered Regularly Interspersed Palindromic Repeats) adaptive immunity system in Streptococcus pyogenes and other bacteria. It uses a guide RNA sequence to cut DNA at a complementary site.