Notes on Genus: Torradovirus

icosahedra

Type member: Tomato torrado virus

General Description

The genus Torradovirus (from the type member Tomato torrado virus) is one of the genera within the plant picornavirus family Secoviridae. It contains viruses reported to be transmitted by whiteflies with three distinct coat protein subunits and an additional ORF at the 5'-end of RNA2 in addition to the polyprotein typical of members of this family.

Morphology

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

Genome

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 (7.8 kb) produces a polyprotein of 241 kDa processed into mature peptides. Cleavage sites have not been determined but these are expected to include a Processing regulator, Nucleotide binding protein, VPg (genome-linked protein), Protease and the RNA-dependent RNA polymerase.

RNA2 (5.4 kb) has a small (20 kDa) ORF predicted near the 5'-terminus and a polyprotein of 134 kDa in which a movement protein can be identified and three separate coat proteins of about 35, 26 and 23 kDa.