Notes on Genus: Norovirus


Type member: Norwalk virus


General Description

This is one of the genera in the family Calicviridae. In common with members of the genus Vesivirus, but in contrast to the other genera, the coat protein is translated from a separate ORF downstream of the large polyprotein. These two genera are distinct in phylogenetic analyses and in this genus the coat protein ORF overlaps slightly the C-terminus of the coat protein.


Virions isometric (icosahedral), not enveloped, 35-40 nm in diameter, made of 90 dimers of the coat protein. There are 32 cup-shaped depressions at each of the fivefold and threefold axes.


Monopartite positive sense single-stranded RNA 7.5-7.7 kb in length with a genome-linked protein (VPg) at the 5'-terminus and a 3'-polyA tail.

Genus Genomic Organization

The RNA encodes a polyprotein that has (from N- to C- termini) helicase, VPg, protease and polymerase domains. A second ORF encodes the coat protein and there is one additional, smaller, ORF.

Type Member Genomic Organization

The genome of about 7,700 nucleotides is translated into:
  1. Polyprotein of 198.7 kDa with (from N- to C- termini) helicase, VPg, protease and polymerase domains
  2. Coat protein of 56.6 kDa
  3. ORF3 (22.5 kDa) of unknown function