ABSTRACT
Genome editing is a useful research tool essentially applicable to gene therapy in the field of biotechnology, pharmaceutics and medicine. Scientists have developed three types of programmable nucleases for genome editing, and these include: Zinc-finger nucleases (ZFNs), transcription activator-like effector nucleases (TALENs), and clustered regularly interspaced short palindromic repeat (CRISPR)-Cas (CRISPR-associated) system particularly derived from bacterial adaptive immune system. Programmable nucleaseses occur double strand breaks (DSBs) on target strand, and a repair mechanism of DSBs introduces either non-homologous end joining (NHEJ) or homology directed repair (HDR), where the pathway is determined by presence of donor DNA template. In this sense, we can generate gene insertion, gene correction, point mutagenesis and chromosomal translocations via endogenous repair mechanism. However, these nucleases exhibit several discrepancies in the aspects of their compositions, targetable sites, efficiency and other characteristics. Here, we discuss on various characteristics of three programmable nucleases and potential outcomes of DSBs. Acknowledging the distinctions among these programmable nucleases will help scientists to select appropriate tools in genome engineering.