Potyviridae: genus Rymovirus.

The genus Rymovirus of the family Potyviridae is comprised of seven rod-shaped viruses with the shared characteristic of being transmitted by mites. Aside from this distinguishing feature, rymoviruses are similar to aphid-transmitted potyviruses in that they share a similar particle morphology, some similar antigenic determinants, similar physico-chemical properties, the ability to induce the formation of cytoplasmic cylindrical inclusions, and the ability to infect only graminaceous hosts. In vitro translation studies with wheat streak mosaic virus (WSMV) suggest that this rymovirus uses a potyviral proteolytic processing strategy to express the 3' terminal capsid protein. At the molecular level, limited nucleotide sequence data for WSMV show similarities with aphid-transmitted potyviruses in the potyviral capsid protein, large nuclear inclusion and cylindrical inclusion regions. Thus, given the similarities between the rymoviruses and the potyviruses, it is appropriate to include this genus within the family Potyviridae.

cDNA cloning and nucleotide sequence of the wheat streak mosaic virus capsid protein gene.

The 3'-terminal region of wheat streak mosaic virus (WSMV) genomic RNA was cloned and a cDNA sequence of 1809 nucleotides upstream of the poly(A) tract was determined. The sequence contains a single open reading frame of 1662 nucleotides and a 3' untranslated region of 147 nucleotides. Translation products from WSMV RNA and WSMV cDNA transcripts were immunoprecipitated by WSMV capsid protein antiserum, indicating that the 3'-terminal region of WSMV RNA encodes the capsid protein. Five potential N-terminal capsid protein protease cleavage sites were identified, which would yield proteins ranging from 31.7K to 46.8K. Alignment of the deduced amino acid sequence of the WSMV capsid protein with those of other potyviruses showed significant, but limited, identity as compared to the alignment of two or more aphid-transmitted potyviruses. Although WSMV has characteristics distinct from potyviruses, because of its particle morphology, translation strategy apparently based on polyprotein processing, the ability to form cytoplasmic cylindrical inclusions and the degree of capsid protein homology with aphid-transmitted potyviruses, it should be considered a member of the potyvirus group.