Notes on Genus: Sadwavirus


Type member: Satsuma dwarf virus


General Description

The genus Sadwavirus (from the type member Satsuma dwarf virus) contains viruses that were previously classified as tentative members of the genus Nepovirus. In common with nepoviruses, its members are characterised by their bipartite genome encapsidated in icosahedral particles with each genome segment producing a polyprotein. However, there are two distinct coat protein subunits of different sizes and phylogenetic analyses suggest the viruses should be classified in a distinct genus within the plant picornavirus family Secoviridae. There is no consistency between current members in the type of vector.


Virions isometric (icosahedral), not enveloped, 26-30 nm in diameter.


Bipartite, linear, single stranded, positive sense RNA. The 3'- terminus of each RNA has a poly(A) tract and the 5'- terminus has a genome-linked protein (VPg).

Genus Genomic Organization

Each RNA is translated into a polyprotein, which is then processed by a series of steps into functional proteins: RNA1 encodes proteins necessary for replication while the cell-to-cell movement protein and coat proteins are encoded on RNA2.

Type Member Genomic Organization

RNA1 (6.8 kb) produces a polyprotein of 230 kDa processed into 5 peptides:
1. Processing regulator
2. Nucleotide binding protein
3. VPg: genome-linked protein
4. Protease
5. Polymerase
RNA2 (5.3 kb) produces a polyprotein of 174 kDa processed into 3 functional peptides:
1. Movement protein
2. Large Coat protein
3. Small coat protein