page_title: RNA silencing suppressor p19
section_title: Structure
hierarchical_section_title: RNA silencing suppressor p19 / Structure
caption_attribution_description: English: The RNA silencing suppressor p19 from the tomato bushy stunt virus, rendered from PDB ID 1R9F. The protein forms a dimer whose two monomers are shown in blue and green. The dimer forms an interaction surface that binds double-stranded RNAs of 19 to 21 base pairs. Plants use RNA silencing as a defense mechanism against viruses; the p19 protein serves as a viral counter-defense that specifically binds siRNAs and suppresses the silencing machinery. Keqiong Ye, Lucy Malinina &amp; Dinshaw J. Patel. Recognition of small interfering RNA by a viral suppressor of RNA silencing. Nature 426, 874-878 (18 December 2003). DOI: 10.1038/nature02213. http://www.nature.com/nature/journal/v426/n6968/full/nature02213.html
context_page_description: RNA silencing suppressor p19 is a protein expressed from the ORF4 gene in the genome of tombusviruses. These viruses are positive-sense single-stranded RNA viruses that infect plant cells, in which RNA silencing forms a widespread and robust antiviral defense system. The p19 protein serves as a counter-defense strategy, specifically binding the 19- to 21-nucleotide double-stranded RNAs that function as small interfering RNA in the RNA silencing system. By sequestering siRNA, p19 suppresses RNA silencing and promotes viral proliferation. The p19 protein is considered a significant virulence factor and a component of an evolutionary arms race between plants and their pathogens.
context_section_description: The p19 protein received its name from its size, being approximately 19 kilodaltons. It forms a functional homodimer. The crystal structures are available of p19 proteins from the tomato bushy stunt virus and Carnation Italian ringspot virus; the protein consists of a novel protein fold and exemplifies a previously unknown mechanism for binding RNA, using a binding surface formed by a beta sheet and flanked by alpha helices to interact with double-stranded RNAs of around 21 nucleotides in length in a non-sequence-specific manner.
caption: The structure of the tomato bushy stunt virus p19 protein bound to double-stranded RNA. The two p19 monomers are shown in blue and green; the RNA backbone is shown in orange. The alpha helices at the top and bottom interact with the ends of the RNA, ensuring that only RNA of the correct length is bound. This has been described as a "molecular caliper".[6] From PDB: 1R9F​.[1]
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