Notes on Genus: Norovirus
Type member: Norwalk virus
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:
- Polyprotein of 198.7 kDa with (from N- to C- termini) helicase, VPg, protease and polymerase domains
- Coat protein of 56.6 kDa
- ORF3 (22.5 kDa) of unknown function