Legoland TALES of Binding DNA by Design

Imagine that you could have a protein that binds to a sequence in a chromosome where you want to activate transcription, nick or break DNA to target insertion or recombination, or create a DNA lesion for screening DNA repair pathway factors…imagine that you could build such proteins very much like putting together legos. Yes, it is possible based on findings about transcription activator-like effector (TALE) proteins. These are plant pathogen transcription factors naturally used to facilitate invasion of host species which have been rekindled to direct DNA binding in other species (1, 2).

Previously, zinc-finger nucleases (ZFNs) have been the focus of genomic modification tool development, but with only limited success. It is not easy to design or select a ZFN using available technologies. In comparison, TALEs have a modular 34 amino acid domain as a basic unit that recognizes a DNA base, with specificity mostly determined by residues 12 and 13. In other words, by using as few as 4 modules with dedicated diamino acids 12 and 13, one can create a protein that binds any DNA sequence.

However, it is not necessarily an easy construct to make because the highly repetitive sequence of TALEs causes plasmid instability during cloning. A team at Harvard recently published a method of minimizing repetitiveness and allowing step-wise ligation; (3). Other aspects of using TALEs involve the designing of an effector domain, e.g. DNAase or transcription activation domain, and packaging the “warhead” in a delivery vehicle such as a lentivirus. The unfolding of the TALEs is just starting, the future seems exciting.

1. J. Boch et al. Science 326, 1509 (2009); published online 29 October 2009
2. M. J. Moscou, and A. J. Bogdanove, Science 326, 1501 (2009)
3. Zhang, F. et al. Efficient construction of sequence-specific TAL effectors for modulating mammalian transcription. Nat. Biotechnol. 29, 149–153 (2011).

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