CRISPR/Cas9 target DNA binding, molecular model. The image shows what is partly inside the CRISPR-associated endonuclease Cas9/Csn1 (not shown for clarity), the single guide RNA (sgRNA, red), the target strand of 18-nucleotide complementary DNA substrate, PAM-proximal end (blue), the target strand of 18-nucleotide complementary DNA substrate, PAM-distal end (cyan) and the non-target strand of 18-nucleotide complementary DNA substrate (green)