Abstract
As a counter-defense against antiviral RNA silencing during infection, the insect Flock House virus (FHV) expresses the silencing suppressor protein B2. Biochemical experiments show that B2 binds to double-stranded RNA (dsRNA) without regard to length and inhibits cleavage of dsRNA by Dicer in vitro. A cocrystal structure reveals that a B2 dimer forms a four-helix bundle that binds to one face of an A-form RNA duplex independently of sequence. These results suggest that B2 blocks both cleavage of the FHV genome by Dicer and incorporation of FHV small interfering RNAs into the RNA-induced silencing complex.
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Acknowledgements
This work was supported by the US National Institutes of Health (grants GM-53320 to J.R.W. and GM-53491 to A.S.), the Skaggs Institute for Chemical Biology and an Achievement Rewards for College Scientists Foundation fellowship to J.A.C. The authors wish to thank E. Sperling for assistance with protein purification, M. Hennig for assistance with NMR spectroscopy and X. Dai, S. Nguyen, S. Ryder, R. Stanfield and R. Williams for helpful discussions.
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Supplementary information
Supplementary Fig. 1
Electrophoretic mobility shift of MBP-B2 with various nucleic acid constructs. (PDF 954 kb)
Supplementary Fig. 2
Experimental electron density map of the B2–dsRNA complex from SeMet MAD phasing (PDF 2970 kb)
Supplementary Fig. 3
Packing of α1 with core of B2 dimer (PDF 1731 kb)
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Chao, J., Lee, J., Chapados, B. et al. Dual modes of RNA-silencing suppression by Flock House virus protein B2. Nat Struct Mol Biol 12, 952–957 (2005). https://doi.org/10.1038/nsmb1005
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DOI: https://doi.org/10.1038/nsmb1005
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