An assembly model of rice dwarf virus particle.

The Phytoreovirus rice dwarf virus (RDV) has a complex nucleocapsid architecture composed of multiple proteins and RNAs. However, specific RNA-protein and protein-protein interactions involved in virion packaging have not been entirely elucidated. In order to define mechanisms governing RDV particle assembly, interactions between individual components were analyzed both in vivo and in vitro. The P7 core protein binds specifically and with high affinity to all 12 genomic RDV dsRNAs. P1, a putative RNA polymerase, P5, a putative guanyltransferase and P7 are encapsidated within the virion and also bind viral transcripts based upon in vitro binding assays. P1, P5, P7 and genomic dsRNAs were lacking in empty particles purified from infected tissues that also yielded fractions containing intact, infectious particles. In addition, P7 forms complexes with P1 and P3, a core capsid protein, in viral particles. These results indicate the possibility that core proteins and dsRNAs interact as one unit suggesting a mechanism for assortment of viral RNAs and subsequent packaging into core particles.