Table 2.

Comparison of site-specific nuclease (SSN) genome editing tools of zinc-finger nucleases (ZFNs), transcription activator-like effector nucleases (TALENs), and clustered regularly interspaced short palindromic repeat (CRISPR)/CRISPR-associated system 9 (Cas9).

SSN system	DNA recognition type	Targeting flexibility	Easy to design and use	Targeting efficiency	Off-targeting effects
ZFN	Protein guide, trimer	+	+	+	++
TALEN	Protein guide, monomer	+++	++	++	+++
CRISRR/Cas9	RNA guide, monomer	+++	+++	+++	+