Structural Basis for Sequence-Specific Recognition of DNA by TAL Effectors

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Science  05 Jan 2012:
DOI: 10.1126/science.1215670


TAL effectors, secreted by phytopathogenic bacteria, recognize host DNA sequences through a central domain of tandem repeats. Each repeat comprises 33 to 35 conserved amino acids and targets a specific base pair using two hypervariable residues (known as RVD) at positions 12 and 13. Here, we report the crystal structures of a 11.5-repeat TAL effector in both DNA-free and DNA-bound states. Each TAL repeat comprises two helices connected by a short RVD-containing loop. The 11.5 repeats form a right-handed, super-helical structure that tracks along the sense strand of DNA duplex, with RVDs contacting the major groove. The 12th residue stabilizes the RVD loop, whereas the 13th residue makes a base-specific contact. Understanding DNA recognition by TAL effectors may facilitate rational design of DNA-binding proteins with biotechnological applications.