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Originally published in Science Express on 29 October 2009
Science 11 December 2009:
Vol. 326. no. 5959, pp. 1509 - 1512
DOI: 10.1126/science.1178811


Breaking the Code of DNA Binding Specificity of TAL-Type III Effectors

Jens Boch,* Heidi Scholze, Sebastian Schornack,{dagger} Angelika Landgraf, Simone Hahn, Sabine Kay,Thomas Lahaye, Anja Nickstadt,{ddagger} Ulla Bonas
The pathogenicity of many bacteria depends on the injection of effector proteins via type III secretion into eukaryotic cells in order to manipulate cellular processes. TAL (transcriptionactivator–like) effectors from plant pathogenic Xanthomonas are important virulence factors that act as transcriptional activators in the plant cell nucleus, where they directly bind to DNA via a central domain of tandem repeats. Here, we show how target DNA specificity of TAL effectors is encoded. Two hypervariable amino acid residues in each repeat recognize one base pair in the target DNA. Recognition sequences of TAL effectors were predicted and experimentally confirmed. The modular protein architecture enabled the construction of artificial effectors with new specificities. Our study describes the functionality of a distinct type of DNA binding domain and allows the design of DNA binding domains for biotechnology.
Department of Genetics, Institute of Biology, Martin-Luther-University Halle-Wittenberg, Weinbergweg 10, D-06099 Halle (Saale) Germany.

{dagger} Present address: Sainsbury Laboratory, John Innes Centre, Norwich, Norfolk NR4 7UH, UK.

{ddagger} Present address: Icon Genetics GmbH, Biozentrum, Weinbergweg 22, D-06120 Halle (Saale), Germany.

* To whom correspondence should be addressed. E-mail:

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Originally published in Science Express on 29 October 2009
Science 11 December 2009:
Vol. 326. no. 5959, p. 1501
DOI: 10.1126/science.1178817


A Simple Cipher Governs DNA Recognition by TAL Effectors

Matthew J. Moscou and Adam J. Bogdanove*
TAL effectors of plant pathogenic bacteria in the genus Xanthomonas bind host DNA and activate genes that contribute to disease or turn on defense. Target specificity depends on an effector-variable number of typically 34 amino acid repeats, but the mechanism of recognition is not understood. We show that a repeat-variable pair of residues specifies the nucleotides in the target site, one pair to one nucleotide, with no apparent context dependence. Our finding represents a previously unknown mechanism for protein-DNA recognition that explains TAL effector specificity, enables target site prediction, and opens prospects for use of TAL effectors in research and biotechnology.
Department of Plant Pathology and Bioinformatics and Computational Biology Program, Iowa State University, Ames, IA 50011, USA.

* To whom correspondence should be addressed. E-mail:

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Science 11 December 2009:
Vol. 326. no. 5959, pp. 1491 - 1492
DOI: 10.1126/science.1183604



DNA Binding Made Easy

Daniel F. Voytas1 and J. Keith Joung2,3,4

All cells encode specific DNA binding proteins that ensure that genetic material is appropriately expressed, replicated, and transmitted from one generation to the next. Mother Nature solved the DNA recognition problem by inventing a handful of protein motifs, including the zinc finger, the helix-turn-helix, and the leucine zipper. As is the case with all good solutions to a problem, these motifs are used over and over again in biological systems; for example, DNA binding proteins containing the helix-turn-helix motif are found in both prokaryotes and eukaryotes, and zinc finger—containing proteins are the most abundant protein class encoded by the human genome. It is surprising, therefore, to learn from studies by Boch et al. (1) on page 1509 and Moscou and Bogdanove (2) on page 1501 of this issue, about a new DNA binding motif that has heretofore escaped description.

1 Department of Genetics, Cell Biology and Development and Center for Genome Engineering, University of Minnesota, Minneapolis, MN 55455, USA.
2 Molecular Pathology Unit and Center for Cancer Research, Massachusetts General Hospital, Charlestown, MA 02129, USA.
3 Center for Computational and Integrative Biology, Massachusetts General Hospital, Boston, MA 02114, USA.
4 Department of Pathology, Harvard Medical School, Boston, MA 02115, USA.


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