Notes on Genus: Betacoronavirus

enveloped spheres
enveloped spheres

Type member: Murine coronavirus


General Description

This is one of the genera in the subfamily Coronavirinae of the family Coronaviridae. Within this subfamily, viruses have spherical virions with club-shaped surface projections and a core shell. The name is from the Latin corona = crown, reflecting the appearance of these projections in electron microscopy. This genus contains what were previously considered phylogroup 2 coronaviruses.


Virions enveloped and spherical 120-160 nm in diameter, with a core shell of about 65nm. The large surface projections are formed by glycoproteins and a trimers of the spike protein.


Monopartite positive sense single-stranded RNA 29-31 kb in length and with a 3'-polyA tail.

Genus Genomic Organization

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. These contain regions with protease, helicase and RNA polymerase motifs. Downstream are up to 9 other genes, most of which encode structural proteins, and these are expressed from a 3'-coterminal nested set of subgenomic RNAs. The major characterised proteins occur in a conserved order and are:
  • Hemagglutinin-esterase protein HE (only in some members)
  • Spike protein S
  • Two to three small non-structural proteins
  • Small envelope protein E
  • Membrane protein M
  • Coat protein N
  • In some viruses there are additional small non-structural proteins between genes M and N or downstream of N

Type Member Genomic Organization

The RNA of 31.3kb is translated into the following products:
  • Replication protein 1a of 491 kDa
  • Polymerase 1b of 309 kDa, expressed as a fusion protein with 1a by ribosomal frameshift
  • Non-structural protein 2a of 31 kDa
  • Hemagglutinin-esterase protein HE of 11 kDa
  • Spike protein S of 150 kDa
  • Non-structural protein 5a of 13 kDa
  • Small envelope protein E of 10 kDa
  • Membrane protein M of 26 kDa
  • Coat protein N of 49 kDa