Notes on Genus: Torovirus
Type member: Equine torovirus
This is one of the genera in the subfamily Torovirinae
of the family Coronaviridae
. Within this subfamily, viruses have pleomorphic virions and no core shell. This genus contains viruses infecting mammals. The name is from the Latin torus
= the lowest convex moulding at the base of a column, reflecting the shape of the nucleocapsid.
Virions enveloped and pleomorphic 120-140 nm in diameter, and apparently without a core shell. There are large surface projections formed by glycoproteins.
Monopartite positive sense single-stranded RNA about 25-30 kb in length and with a 3'-polyA tail.
Genus Genomic Organization
There are two large, overlapping ORFs at the 5'-end of the genome encode the major non-structural proteins and these are expressed as a fusion protein by ribosomal frameshift. They contain regions with protease, helicase and RNA polymerase motifs. Downstream are 4 other genes encoding structural proteins and expressed from a 3'-coterminal nested set of subgenomic RNAs. In Bovine torovirus, these products are:
- Replication protein 1a, 505.9 kDa
- Polymerase fusion protein, 765.9 kDa
- Spike protein S, 177.9 kDa
- Membrane protein M, 26.4 kDa
- Hemagglutinin-esterase protein HE, 46.7 kDa
- Coat protein N, 18.9 kDa
Type Member Genomic Organization
There is no complete sequence of the type member.