Abstract
TAL (transcription activator-like) effectors are translocated by Xanthomonas bacteria into plant cells where they activate transcription of target genes. DNA target sequence recognition occurs in a unique mode involving a central domain of tandem repeats. Each repeat recognizes a single base pair in a contiguous DNA sequence and a pair of adjacent hypervariable amino acid residues per repeat specifies which base is bound. Rearranging the repeats allows the design of novel TAL proteins with predictable DNA-recognition specificities. TAL protein-based transcriptional activation in plant cells is mediated by a C-terminal activation domain (AD). Here, we created synthetic TAL proteins with designed repeat compositions using a novel modular cloning strategy termed “Golden TAL Technology”. Newly programmed TAL proteins were not only functional in plant cells, but also in human cells and activated targeted expression of exogenous as well as endogenous genes. Transcriptional activation in different human cell lines was markedly improved by replacing the TAL-AD with the VP16-AD of herpes simplex virus. The creation of TAL proteins with potentially any desired DNA-recognition specificity allows their versatile use in biotechnology.
Highlights
Transcription activator-like (TAL) effectors include key virulence factors of Xanthomonas that bind to promoter regions of plant genes and act as DNA sequence-specific transcriptional activators [1,2,3,4]
To generate TAL proteins with a potential transcription factor activity in non-plant organisms, we deleted the activation domain (AD) from the TAL effectors AvrBs3 and Hax3 and replaced them with the ADs of the herpes simplex virus (HSV) VP16 and the yeast GAL4 transcription activators, respectively (Figure S1A)
In this report we demonstrate that TAL protein derivatives can be used to modulate the transcription of genes in human cells
Summary
Transcription activator-like (TAL) effectors include key virulence factors of Xanthomonas that bind to promoter regions of plant genes and act as DNA sequence-specific transcriptional activators [1,2,3,4]. TAL effectors contain a central domain of tandem repeats (1 to 33.5 repeats of typically 34 amino acids) [1]. One repeat corresponds to one DNA base pair, and the specificity of each repeat is encoded by two hypervariable amino acids (position 12 and 13) per repeat, termed repeat-variable diresidue (RVD) [7,8]. Based on the repeat-specificity code, the target DNA specificities of several TAL effectors were correctly predicted [7,9,10]. The modular architecture, a hallmark of the TAL protein repeat domain, enables simple rearrangements of desired repeat orders. TAL proteins with novel and clearly predictable DNA-recognition specificities can be constructed [7,12,13,14,15,16,17]
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