Notes on Genus: Torovirus

enveloped spheres
enveloped spheres

Type member: Equine torovirus


General Description

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.