The p19 siRNA Binding Protein (19 kDa) from the Carnation Italian Ringspot Virus (CIRV) plant binds siRNAs with nanomolar affinity

The dimeric protein binds 21 base siRNAs with a 2 base 3′ extension and a 5′phosphate. The protein binds RNA in a size dependent and sequence independent manner. If the siRNAs are 4 bases longer, the affinity for the protein is reduced about 100-fold. When p19 siRNA Binding Protein is expressed in plants it suppresses RNA interference.