The working principle of this system is that crRNA(CRISPR-pried RNA) binds to tracrRNA/crRNA by base pairing to form a tracrRNA/crRNA complex, which directs the nuclease Cas9 protein to be paired with crRNA. The sequence target point cuts double-stranded DNA. Through the artificial design of these two RNAs, sgRNA(sigle-Guide RNA) can be modified to form a guiding effect, which is sufficient to guide Cas9's fixed-point DNA cutting.
As an RNA-guided dsDNA binding protein, Cas9 effect nuclease is the first known unifying factor that can collectively locate RNA, DNA, and proteins, thus having great potential for transformation. The protein is fused with Cas9 nuclease-free Cas9 and expresses an appropriate sgRNA that can target any dsDNA sequence, and the end of the sgRNA can be attached to the target DNA without affecting the binding of Cas9. Therefore, Cas9 can bring any fusion protein and RNA to any dsDNA sequence, which has great potential for research and transformation of organisms.