STRUCTURE OF DOUBLE-SHELLED RICE DWARF VIRUS

Rice dwarf virus (RDV), a member of the Reoviridae family, is a double -stranded RNA virus. Infection of rice plants with RDV reduces crop pr oduction significantly and can pose a major economic threat to Southea st Asia. A 25-Angstrom three-dimensional structure of the 700-Angstrom -diameter RDV capsid has been determined by 400-kV electron cryomicros copy and computer reconstruction. The structure revealed two distincti ve icosahedral shells: a T=13l outer icosahedral shell composed of 260 trimeric clusters of P8 (46 kDa) and an inner T=1 icosahedral shell o f 60 dimers of P3 (114 kDa). Sequence and structural comparisons were made between the RDV outer shell trimer and the two crystal conformati ons (REF and HEX) of the VP7 trimer of bluetongue virus, an animal ana log of RDV, The low-resolution structural match of the RDV outer shell trimer to the HEX conformation of VP7 trimer has led to the proposal that P8 consists of an upper domain of P-sandwich motif and a lower do main of alpha helices, The less well fit REF conformation of VP7 to th e RDV trimer may be due to the differences between VP7 and P8 in the s equence of the hinge region that connects the two domains, The additio nal mass density and the absence of a known signaling peptide on the s urface of the RDV outer shell trimer may be responsible for the differ ent interactions between plants and animal reoviruses.