TALENs^™ are new genome customization tools that can be used for gene-specific modifications and disruptions.

TALEs were first discovered in the plant pathogen, Xanthomonas. TALEs specifically bind to DNA and regulate plant genes during infection by the pathogen.

Each TALE contains a central repetitive region consisting of varying numbers of repeat units of typically 33-35 amino acids. It is this repeat domain that is responsible for specific DNA sequence recognition. Each repeat is almost identical with the exception of two variable amino acids termed the repeat-variable diresidues. The mechanism of DNA recognition is based on a code where one nucleotide of the DNA target site is recognized by the repeat-variable diresidues of one repeat.

A TALEN^TM is composed of a TALE DNA binding domain for sequence-specific recognition fused to the catalytic domain of an endonuclease that introduces double strand breaks (DSB). The DNA binding domain of a TALEN^TM is capable of targeting with high precision a large recognition site (for instance 17bp).

A TALEN^TM is defined as a heterodimer (2 units of a TALE DNA binding domain fused to a catalytic domain) cleaving two close sequences, resulting in increased specificity.

DSB can be repaired by one of two pathways:

• Homologous Recombination (HR): HR is stimulated by a double strand break, and in the presence of a template, specific DNA changes can be made and transgenes can be integrated.
• Non Homologous End Joining (NHEJ): NHEJ is a natural repair mechanism that can be used to introduce nucleotide deletions to inactivate or knock-out a specific target gene.

Very recently, publications have demonstrated TALENs efficiency and potential for a use in genome customization:

• Knockout rats generated by embryo microinjection of TALENs. Tesson L., et al. Nature Biotechnology 29
• Targeted gene disruption in somatic zebrafish cells using engineered TALENs. Sander J.D., et al. Nature Biotechnology 29, 697-698, August 2011
• Heritable gene targeting  in zebrafish using customized TALENs. Huang P., et al. Nature Biotechnology 29, 699-700, August 2011
• Targeted genome editing across species using ZFNs and TALENs. Wood A.J., et al. SCience July; 333(6040):307
• A novel TALE nuclease scaffold enables high genome editing activity in combination with low toxicity. Mussolino C., et al. Nucleic Acids Research, August 2011.
• Assembly of TALE-type DNA binding domaines by modular cloning. Morbitzer R., et al. Nucleic Acids Research, July 2011, 39(13):5790-9 
• TAL nucleases (TALNs): hybrid proteins composed of TAL effectors and FokI DNA-cleavage domain. Ting Li, et al. Nucleic Acids Research, 2011, Vol. 39, No. 1 359-372
• Efficient construction of sequence-specific TAL effectors for modulating mammalian transcription. Feng Zhang, et al. Nature biotechnology Letters: published online 19 January 2011; doi: 10.1038/nbt1775
• Targeting DNA Double-Strand Breaks with TAL Effector Nucleases. Michelle Christian, et al. Genetics 186: 757-761 (October 2010)
• De novo-engineered transcription activator-like effector (TALE) hybrid nuclease with novel DNA binding specificity creates double-strand breaks. Magdy M. Mahfouz, et al. Proc Natl Acad Sci U S A. 2011 Jan 24.
• A TALE nuclease architecture for efficient genome editing. Jeffrey. C. Miller, et al. Nature biotechnology Articles: published online 22 December 2010

Access the Nature Collections issue on Nature Biotechnology for a comprehensive list of recent publications on TALENs.

> To enquire about the TAL Effector Nucleases, feel free to contact us. 

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