Figure 4.

Major applications of Cas9, dCas9, and Cpf1 in genome editing. The three widely accepted CRISPR-dependent systems (A–C) broadly complement each other, even though the specified usage are not always restricted to individual proteins, i.e., Cas9 (A) and Cpf1 (C) can substitute each other to perform at least some of the mentioned tasks. Both enzymes require unique protospacer adjacent motif (PAM) to locate the gene of interest, making them complementary when no proper PAM is available for any of them. RNA-guided double-strand break is vital to their functioning. Whereas, Cas9 incision generates blunt ends, Cpf1 produces cohesive ends. The dCas9 (B) method can recompense for Cas9, when the target genomic loci happen to be essential. The inactivated isoform of Cas9 serves as a blocker, enabling a silencing of gene transcription instead of disrupting the gene locus. Its low toxicity also allows the assembly of stable progenitor lines for successive transgenic research. Not least, the feature that dCas9 can bind harmlessly to a locus of interest permits a fusion of dCas9 with reporter or effector proteins, further expanding its utility to epigenetic and epigenomic studies. Cas9, CRISPR associated protein 9; Cpf1, Centromere and Promoter Factor 1; dCas9, catalytically dead Cas9; cr-RNA, CRISPR-RNA; Indel, insert or deletion (of bases in the genome).