TAL effector nucleases are customized DNA scissors that bind and cleave pre-selected DNA sequences. The first TALEN® was developed through a collaboration between the laboratories of Dr. Dan Voytas (CSO at Calyxt) and Dr. Adam Bogdanove at University of Minnesota and Iowa State University, respectively, in 2009. A functional TALEN® consists of a DNA binding domain, which is derived from transcription activator-like effector (TALE) proteins and a nuclease catalytic domain from a DNA nuclease, FokI. The DNA binding domain of TALE features an array of 33 or 34-amino acid repeats. Each repeat is highly conserved, with the exception of the so-called repeat variable di-residues (RVDs) at amino acid positions 12 and 13. The RVDs determine which nucleotide each repeat recognizes within the targeted DNA sequence. The simple one-to-one correspondence between TALE repeat binding to nucleotides in DNA sequences make it a straightforward process to assemble repeat arrays to recognize novel DNA sequences. There are no apparent limits to the targeting range of a customized TALEN®. At least one TALEN® target site can be identified in every 10-20 base pairs in any genome. Together, these features make TALEN® the most powerful tool in the current genome engineering field to date. Calyxt has implemented this nuclease engineering tool to produce the best-in-class plant genome modification platform.
Key Advantages of TALEN® Over Other Gene-Editing Technologies
In addition to TALEN®, we are aware of three other classes of nucleases that enable gene editing, including meganucleases, zinc finger nucleases and CRISPR/Cas9. Despite the availability of other gene-editing platforms, we currently rely on TALEN® because of the following benefits: