Fig. 2.

Schematic of the gene tools based on Cas9, nCas9, and dCas9, respectively. a The HR system is used to accurately repair the DSBs introduced by Cas9 protein or the single-strand breaks introduced by nCas9 protein when donor DNA fragments are provided. The NHEJ system is used to inaccurately repair the DSBs introduced by Cas9 protein when Donor DNA fragments are not provided. b The combination of dCas9 and the target site inhibits the combination of RNAP and the DNA strand, which weakens the DNA transcription process and reduces the expression of the targeted gene. The expression of a fusion protein comprising dCas9 and a transactivator domain can recruit RNAP and enhance the process of DNA transcription, thus increasing targeted gene expression. The red dots in A/B represent gene mutations in the corresponding cleavage domains