Table 3.
Comparison of three engineered endonucleases-ZFN, TALEN, and CRISPR/Cas9.
| ZFN | TALEN | CRISPR/Cas9 | |
|---|---|---|---|
| Target sequence | 9–18 bp per ZFN monomer | 15–20 bp per TALEN monomer | 20 bp plus PAM sequence |
| Mode of recognition | Protein:DNA | Protein:DNA | RNA:DNA |
| Endonuclease | FokI | FokI | Cas |
| Delivery | Two ZFNs around the target sequence are required | Two TALENs around the target sequence are required | sgRNA with Cas9 |
| Construction | Zinc finger sequence specifically recognizing 3-nucleotide sequence linked to FokI | Protein sequence specifically recognizing 1-nucleotide sequence linked to FokI | 20-nucleotide sgRNA complementary to the target sequence fused to Cas9 |
| Reprogramming efficiency | Relatively low | Relatively low | High (easy to design, fast to synthesize) |
| Off-target effects | High | Low | Variable |