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Repeat 1 of TAL effectors affects target specificity for the base at position zero.

Schreiber T, Bonas U - Nucleic Acids Res. (2014)

Bottom Line: AvrBs3, the founding member of the Xanthomonas transcription-activator-like effectors (TALEs), is translocated into the plant cell where it localizes to the nucleus and acts as transcription factor.T0 and W232 appear to be particularly important if the RVD of the first repeat is HD ('rep1 effect').Our findings provide novel insights into the mechanism of T0 recognition by TALE proteins and are important for TALE-based biotechnological applications.

View Article: PubMed Central - PubMed

Affiliation: Department of Genetics, Martin Luther University, Weinbergweg 10, 06120 Halle (Saale), Germany tom.schreiber@genetik.uni-halle.de.

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Model of T0-coordination by TALE proteins. TALE repeats are coordinated along the sugar-phosphate backbone of the DNA sense strand. Degenerated repeats are indicated in gray, canonical repeats are indicated in yellow and light yellow. (A) Upon DNA target scanning the canonical repeats shift laterally and vertically (red arrows) due to sterical clashes between residue 13 and non-matching bases. Thymine, which interacts with tryptophan (W232) stabilizes the interaction between RVD1 and base 1. (B) Once the target sequence is bound W232 and T0 facilitates interaction of RVD1 and N1. Specific interactions of RVDs and matching bases lead to compression of the canonical repeats. Necessity of specific RVD-base interactions (indicated in red) decreases from 5′ to 3′. (C) Compression of the canonical repeats induce conformational switch of the NTR, leading to exposure of R236 and R266 in the major groove.
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Figure 7: Model of T0-coordination by TALE proteins. TALE repeats are coordinated along the sugar-phosphate backbone of the DNA sense strand. Degenerated repeats are indicated in gray, canonical repeats are indicated in yellow and light yellow. (A) Upon DNA target scanning the canonical repeats shift laterally and vertically (red arrows) due to sterical clashes between residue 13 and non-matching bases. Thymine, which interacts with tryptophan (W232) stabilizes the interaction between RVD1 and base 1. (B) Once the target sequence is bound W232 and T0 facilitates interaction of RVD1 and N1. Specific interactions of RVDs and matching bases lead to compression of the canonical repeats. Necessity of specific RVD-base interactions (indicated in red) decreases from 5′ to 3′. (C) Compression of the canonical repeats induce conformational switch of the NTR, leading to exposure of R236 and R266 in the major groove.

Mentions: Previously, it was suggested that the NTRs of TALEs serve as nucleation site for the DNA interaction (9,24). To integrate our data we propose the following model (Figure 7). TALEs may slide along the DNA scanning for the target sequence. Once the target sequence is reached, specific contacts between the canonical repeats and nucleobases occur from 5′ to 3′ and allow the repeats to compress (8,9,24). Taking this idea into account we hypothesize that the W232-T0 interaction facilitates the specific interaction between canonical repeats and target nucleobases which may be more crucial if an HD1 contact to C1 needs to be established (Figure 7). We can only speculate about the strong dependency of TALEs with HD1 on T0 and W232. One explanation could be that the amine group of cytosine targeted by HD is more distant from the sugar phosphate backbone than N7 of guanine and adenine or the methyl group of thymine targeted by other RVDs (Supplementary Figure S10). In addition, HD is the only RVD which accepts the hydrogen bond from the base, whereas others donate hydrogen bonds to the base or interact with the base via van der Waals forces (Supplementary Figure S10) (8,10,26).


Repeat 1 of TAL effectors affects target specificity for the base at position zero.

Schreiber T, Bonas U - Nucleic Acids Res. (2014)

Model of T0-coordination by TALE proteins. TALE repeats are coordinated along the sugar-phosphate backbone of the DNA sense strand. Degenerated repeats are indicated in gray, canonical repeats are indicated in yellow and light yellow. (A) Upon DNA target scanning the canonical repeats shift laterally and vertically (red arrows) due to sterical clashes between residue 13 and non-matching bases. Thymine, which interacts with tryptophan (W232) stabilizes the interaction between RVD1 and base 1. (B) Once the target sequence is bound W232 and T0 facilitates interaction of RVD1 and N1. Specific interactions of RVDs and matching bases lead to compression of the canonical repeats. Necessity of specific RVD-base interactions (indicated in red) decreases from 5′ to 3′. (C) Compression of the canonical repeats induce conformational switch of the NTR, leading to exposure of R236 and R266 in the major groove.
© Copyright Policy - creative-commons
Related In: Results  -  Collection

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Show All Figures
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Figure 7: Model of T0-coordination by TALE proteins. TALE repeats are coordinated along the sugar-phosphate backbone of the DNA sense strand. Degenerated repeats are indicated in gray, canonical repeats are indicated in yellow and light yellow. (A) Upon DNA target scanning the canonical repeats shift laterally and vertically (red arrows) due to sterical clashes between residue 13 and non-matching bases. Thymine, which interacts with tryptophan (W232) stabilizes the interaction between RVD1 and base 1. (B) Once the target sequence is bound W232 and T0 facilitates interaction of RVD1 and N1. Specific interactions of RVDs and matching bases lead to compression of the canonical repeats. Necessity of specific RVD-base interactions (indicated in red) decreases from 5′ to 3′. (C) Compression of the canonical repeats induce conformational switch of the NTR, leading to exposure of R236 and R266 in the major groove.
Mentions: Previously, it was suggested that the NTRs of TALEs serve as nucleation site for the DNA interaction (9,24). To integrate our data we propose the following model (Figure 7). TALEs may slide along the DNA scanning for the target sequence. Once the target sequence is reached, specific contacts between the canonical repeats and nucleobases occur from 5′ to 3′ and allow the repeats to compress (8,9,24). Taking this idea into account we hypothesize that the W232-T0 interaction facilitates the specific interaction between canonical repeats and target nucleobases which may be more crucial if an HD1 contact to C1 needs to be established (Figure 7). We can only speculate about the strong dependency of TALEs with HD1 on T0 and W232. One explanation could be that the amine group of cytosine targeted by HD is more distant from the sugar phosphate backbone than N7 of guanine and adenine or the methyl group of thymine targeted by other RVDs (Supplementary Figure S10). In addition, HD is the only RVD which accepts the hydrogen bond from the base, whereas others donate hydrogen bonds to the base or interact with the base via van der Waals forces (Supplementary Figure S10) (8,10,26).

Bottom Line: AvrBs3, the founding member of the Xanthomonas transcription-activator-like effectors (TALEs), is translocated into the plant cell where it localizes to the nucleus and acts as transcription factor.T0 and W232 appear to be particularly important if the RVD of the first repeat is HD ('rep1 effect').Our findings provide novel insights into the mechanism of T0 recognition by TALE proteins and are important for TALE-based biotechnological applications.

View Article: PubMed Central - PubMed

Affiliation: Department of Genetics, Martin Luther University, Weinbergweg 10, 06120 Halle (Saale), Germany tom.schreiber@genetik.uni-halle.de.

Show MeSH
Related in: MedlinePlus