July 2012: New update on a high-efficiency guanine-specific RVD (“NH”) (PubMed Central).

June 2012:  Have a question? Check out the new TALE Discussion Forum.

March 2012: Using PlasmidSafe before transforming ligation products greatly increases the yield of correctly assembled TALEs. Updated online protocol here.


Introduction to TAL Effectors

Transcription activator like effectors (TALEs) are natural type III effector proteins secreted by nutmerous species of Xanthomonas to modulate gene expression in host plants and to facilitate bacterial colonization and survival (Boch et al., Annu Rev Phytopathol 2010; Bogdanove et al., Curr Opin Plant Biol 2010). Recent studies of TALEs have revealed an elegant code linking the repetitive region of TALEs with their target DNA-binding site (Boch et al., Science 2009; Moscou et al., Science 2009). Common among the entire family of TALEs is a highly conserved and repetitive region within the middle of the protein, consisting of tandem repeats of mostly 33 or 34 amino acid segments. Repeat monomers differ from each other mainly in amino acid positions 12 and 13 (repeat variable di-residues), and recent computational and functional analyses have revealed a strong correlation between unique pairs of amino acids at positions 12 and 13 and the corresponding nucleotide in the TALE-binding site: NI to A, HD to C, NG to T, NN to G (and to a lesser degree A) (Boch et al., Science 2009Moscou et al., Science 2009; Miller et al., Nat. Biotech 2011Zhang et al., Nat. Biotech 2011).

The simplicity of the TALE code opens many opportunities for biological applications (Boch, Nat. Biotechnol 2011; Rusk, Nat. Methods 2011). Recent studies have tested the modularity of the TALE DNA binding code and have demonstrated that custom TALEs can be designed to recognize specific DNA sequences in a number of different cell types including plant and mammalian cells (Scholze et al., Virulence 2010; Morbitzer et al., PNAS 2010; Miller et al., Nat. Biotech 2010; Zhang et al., Nat. Biotech 2011). Custom TALEs can be tethered to a variety of effector domains to modulate transcription of endogenous genes in the genome (Morbitzer et al., PNAS 2010; Miller et al., Nat. Biotech 2010; Zhang et al., Nat. Biotech 2011) as well as generate site-specific double strand break to catalyze homologous recombination for genome engineering applications (Christian et al., Genetics 2010; Miller et al., Nat. Biotech 2010; Li et al. Nucleic Acids Res 2011; Mahfouz et al., PNAS 2011).

These pages include protocols as well as reagents for constructing custom TALEs as well as deploying TALEs in experimental applications (Sanjana, Cong, Zhou et al., Nature Protocols 2012Zhang, Cong et al., Nature Biotechnology 2011). You will also find a full list of reviews and relevant studies in the references section.