Notes on Genus: Tobravirus

rigid rods

Type member: Tobacco rattle virus

Contents

Members of this Genus
General Description
Morphology
Electron Micrograph
Genome
Genus Genomic Organization
Genome Map
Type Member Genomic Organization
All Known Sequences
Curated Sequences

General Description

The genus Tobravirus (tobacco rattle virus group) is characterised by its rod-shaped particles of two modal lengths, a bipartite genome, and transmission by nematodes in the genera Trichodorus and Paratrichodorus.

Morphology

Virions rod-shaped, not enveloped, usually straight, with distinct central canal and of two modal lengths: L, 180-215 nm long and S, 46-115 nm. Many strains also produce small amounts of shorter particles. Particle diameter 20-23 nm). Symmetry helical with pitch of 2.5 nm.

Genome

Bipartite, linear, single stranded, positive sense RNA. RNA1 is about 6800 nucleotides, while RNA2 varies between 1800 and 4500. The 3' terminus has no poly(A) tract. The 5' terminus has a methylated nucleotide cap with the sequence m7G5'ppp5'Ap.

Genus Genomic Organization

RNA1 encodes four non-structural proteins, including those involved in replication and movement, while RNA2 encodes the coat protein (22-24 kDa), and (in some virus strains) up to three non-structural proteins, at least one of which (29-40 kDa) is required for nematode transmission. In many isolates, the 3'-terminus of RNA2 consists of sequence derived from RNA1.

Type Member Genomic Organization

RNA1 encodes four non-structural proteins:
1. 134 kDa Replication proteincontaining methyl transferase and helicase motifs
2. 194 kDa Poymerase readthrough incorporating RdRp domain
3. 29 kDaMovement protein, expressed from 3'-coterminal subgenomic mRNA 1a
4. 16 kDaCysteine-rich protein of unknown function, expressed from a 3'-coterminal subgenomic mRNA 1b

RNA2 encodes the coat protein and, depending on the isolate, up to 3 non-structural proteins, all translated from subgenomic mRNAs:
5. 23 kDa Coat protein: present in all isolates
9 kDa k gene protein, present in a few isolates (e.g. Rostock; Tp01)
6. 27-40 kDaNematode transmission protein 2b, present in most isolates (but not PSG, PLB and Rostock)
7. 18-33 kDa2c protein, unknown function
In some strains (e.g. TCM), the 3'-end of RNA1 consists of some or all of the 1a (29 kDa) and 1b (16 kDa) genes from RNA1, but it is not known if these are expressed from RNA2.