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Cell. 2003 Dec 26;115(7):799-811.

Size selective recognition of siRNA by an RNA silencing suppressor.

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Laboratory of Structural Biology, National Institute of Environmental Health Sciences, National Institutes of Health, Research Triangle Park, NC 27709, USA.


RNA silencing in plants likely exists as a defense mechanism against molecular parasites such as RNA viruses, retrotransposons, and transgenes. As a result, many plant viruses have adapted mechanisms to evade and suppress gene silencing. Tombusviruses express a 19 kDa protein (p19), which has been shown to suppress RNA silencing in vivo and bind silencing-generated and synthetic small interfering RNAs (siRNAs) in vitro. Here we report the 2.5 A crystal structure of p19 from the Carnation Italian ringspot virus (CIRV) bound to a 21 nt siRNA and demonstrate in biochemical and in vivo assays that CIRV p19 protein acts as a molecular caliper to specifically select siRNAs based on the length of the duplex region of the RNA.

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