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Fig. 2 | Cell & Bioscience

Fig. 2

From: Application of CRISPR/Cas9 for biomedical discoveries

Fig. 2

Mechanism of Cas9 action. a The three essential components necessary for CRISPR/Cas activity, using spCas9 as an example, are Cas9, crRNA and tracrRNA. The introduction of the linker region to combine the crRNA and tracrRNA into a single guide RNA (sgRNA) improves overall targeting efficiency. b Recognition of the protospacer region by the sgRNA in conjunction with Cas9 recognition of the appropriate PAM sequence initiates cleavage. c Cleaved DNA fragments. d Mutated forms of Cas9 can contain a single active domain to act as a Cas9n “nickase” where only one strand of the DNA is cleaved. e Alternatively both catalytic domains can be mutated to form a dCas9 “dead” nuclease that can then be tethered to effector molecules to target repression or activation, KRAB and VP64 respectively, for example. Images adapted from

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