Notes on Family: Caliciviridae

icosahedra
icosahedra

Contents

General Description

This family consists of viruses that infect vertebrates and which have isometric virions (35-40 nm) and a monopartite ssRNA genome which encodes a polyprotein and one or two smaller ORFs. It is of interest to plant virologists because there are some similarities to the picornavirus "'superfamily"", including the plant virus families Sequiviridae, Comoviridae and Potyviridae. The name is from the Latin calix (= cup) because of the distinctive cup-shaped depressions in the virion surface.

Morphology

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.

Genomen

Monopartite positive sense single-stranded RNA 7.4-8.3 kb in length with a genome-linked protein (VPg) at the 5'-terminus and a 3'-polyA tail. It encodes a polyprotein that has helicase, VPg, protease and polymerase domains. In some genera, the coat protein is at the C-terminus of the polyprotein, while in others it is encoded by a separate ORF. There is usually an additional small ORF encoding a basic protein of unknown function.

Genera in the Family

  • Lagovirus (coat protein at C-terminus of polyprotein; infecting rabbits and hares)
  • Nebovirus (coat protein at C-terminus of polyprotein; infecting cattle)
  • Norovirus (coat protein translated from a separate ORF overlapping with the polyprotein)
  • Sapovirus (coat protein at C-terminus of polyprotein; causing gastroenteritis in humans)
  • Vesivirus (coat protein translated from a separate ORF following the polyprotein)