Molecular aspects of TAL effector-DNA binding

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Natural TAL effectors (TALEs) from plant-pathogenic Xanthomonas spp. bacteria act as transcription factors in plant cells. They employ a repetitive DNA-binding domain with predictable and programmable specificity. Two neighboring amino acids per repeat, termed repeat variable diresidues (RVDs), specify which DNA base is bound. This unique and novel DNA-binding mode has enabled construction of designer TALE derivatives for targeted expression, control of genetic circuits, and chirurgic genome editing with far reaching possibilities for basic science and biotechnology. In this proposal we aim to clarify several molecular parameters of TALE-DNA binding. First, we will analyze novel RVD specificities and their efficiencies, the minimal number and exact position required for strong RVDs, and the impact of mismatches in the target binding sequence. To further understand the molecular basis of these rules, DNA binding of artificial TALEs with different RVDs will be quantified using surface plasmon resonance and microscale thermophoresis. Finally, unusual natural TALE repeats and repeats from TALE homologs will be analyzed for DNA binding to understand how the amino acid backbone of TALE repeats can be modified without losing DNA-binding activity. These studies will clarify rules underlying TALE-DNA-interaction, and help to generally understand binding of repetitive proteins to nucleic acids.