Notes on Genus: Sadwavirus
Type member: Satsuma dwarf virus
The genus Sadwavirus
(from the type member Sa
rf 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|
|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|