TALEN structure is largely similar to zinc-finger nucleases (ZFNs) in that they are composed of heterodimers of a DNA binding domain and the nuclease of the FokI restriction endonuclease. However, instead of using a zinc-finger protein for DNA binding, they use Transcription Activator-Like Effector (TALEs), which were originally identified in plant pathogenic bacteria. TALEN technology consists of tandem repeats of 33-35 amino acids, of which each binds to a single DNA base-pair. TALEN genome editing has become more prevalent than the use of ZFNs, as they overcome a number of obstacles such as decreased cytotoxicity and the ability to target nearly any DNA sequence. Some studies also indicate that they have reduced off-target mutation rates and mediate higher homology-directed repair compared to other site-specific nucleases, including CRISPR/Cas9. There have been a number of studies that have successfully utilized TALEN technology in hPSCs. Like ZFNs, this technology has also been used in combination with the piggyBac™ system to facilitate seamless removal of the donor cassette. TALENs have also been used in combination with single-stranded Oligodeoxynucleotides (ssODNs) to create point mutations in the genome. This technology continues to be a popular choice for gene editing, because unlike ZFNs or CRISPR/Cas9, TALENs can bind to nearly any DNA sequence. This therefore provides a clear advantage for nuclease-design strategies.

Singh et al. (2015) Gene Editing in Human Pluripotent Stem Cells: Choosing the Correct Path. J Stem Cell Regen Biol.