Notes on Family: Tombusviridae

icosahedra

Contents

Members of this Family
General Description
Morphology
Genome
Genera in the Family
All Known Sequences
Curated Sequences

General Description

This family is characterised by its icosahedral particles, a ssRNA genome with (usually) five open reading frames (some of which are expressed from subgenomic RNAs) and transmission through soil or water. The genera have different genome structures and there is little nucleotide similarity between viruses of different genera.

Morphology

Virions isometric and icosahedral (T=3), not enveloped, 28-34 nm in diameter. Nucleocapsids with obvious regular surface structure (of granular appearance). 32 capsomeres per nucleocapsid (virion composed of 180 protein subunits).

Particles contain 17 % nucleic acid.

Genome

Monopartite (except Dianthovirus), linear single stranded positive sense RNA. Total genome 4000-5400 nucleotides long. 3' terminus has no poly (A) tract. 5' terminus probably has a methylated nucleotide cap but this has been demonstrated only in some members.

Genera in the Family

Genera are distinguished by genome organization and also by phylogenetic analysis of the replication and movement proteins.
GenusVirion
size (nm)
Genome (kb)ORFs CP (kDa)CP at 3'-end?
Aureusvirus 30 4.45 40-41no
Avenavirus 35 4.44 48yes
Carmovirus c.30 3.7-4.35 37-42yes
Dianthovirus 31-34 bipartite3or 4+1 37-38sometimes
Gallantivirus 28 3.85 37yes
Macanavirus 28 4.05 37yes
Machlomovirus 30 4.46 25yes Insect vector
Alphanecrovirus 28 3.6-3.75 or 6 27-30sometimes Fungus vector
Betanecrovirus 28 3.6-3.75 or 6 27-30sometimes Fungus vector
Panicovirus 25-30 4.36 26yes
Tombusvirus c.30 4.7-4.85 40-42no
Zeavirus c.30 4.15 27no