Notes on Family: Coronaviridae
This family is grouped with the Arteriviridae
to form the order Nidovirales
. All members of the order have enveloped particles containing a single species of single-stranded RNA that encodes for a number of proteins by means of a series of nested (Latin Nido
= nest) subgenomic RNAs. The family Coronaviridae
contains those members with spherical or pleomorphic virions more than 100nm in diameter (those of the family Arteriviridae
are only 45-60nm) and which infect vertebrates. The family Roniviridae
consists of viruses with bacilliform particles that infect crustaceans.
Virions enveloped and spherical or pleomorphic 120-160 nm in diameter.
Monopartite positive sense single-stranded RNA of size >20kb and with a 3'-polyA tail. Two large, overlapping ORFs at the 5'-end of the genome encode the major non-structural proteins and are expressed as a fusion protein by ribosomal frameshift. Downstream are up to 9 other genes, mostly or entirely encoding structural proteins, and these are expressed from a 3'-coterminal nested set of subgenomic RNAs.
Genera in the Family
- Subfamily Coronavirinae: virions spherical with club-shaped projections and a core shell. Genera form distinct monophyletic groups:
- Subfamily Torovirinae: virions pleomorphic without a core shell; tubular nuclecapsid with helical symmetry. Genera form distinct monophyletic groups and have different types of host: