Figure 7.

Schematic illustration of on–off regulation of genome editing by a flap-type aptamer. The Cas9 protein (light orange) assembles with the crRNA (blue) and tracrRNA (purple) to bind genomic DNA with a PAM sequence (yellow). In the absence of the inhibitory aptamer, the switch is on, resulting in genomic DNA editing. However, in the presence of the aptamer, the binding site is occupied by the aptamer that also contains a competitive PAM sequence (CGG). Four nucleotides in the flap region (red) of the aptamer form a complementary duplex with the crRNA seed sequence (blue). Consequently, Cas9’s target DNA binding and complementary base pairing between target DNA and crRNA are inhibited, and the switch is turned off.