Notes on Genus: Sobemovirus

icosahedra

Type member: Southern bean mosaic 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 Sobemovirus (named from the type member, southern bean mosaic virus) has isometric particles of about 30 nm in diameter and a monopartite genome. They have some similarities to the members of the family Tombusviridae in size of virion and genome but they differ in the molecular weights of their capsid proteins and in genome organisation. Most of the better know members (but not all) are beetle-transmitted, and some are also transmitted through seed.

Some sobemoviruses encapsidate a viroid-like Circular satellite RNA of 220-390nt, which is dependent on the helper virus for replication.

Morphology

Virions isometric (icosahedral), not enveloped, 30 nm in diameter. The surface capsomere arrangement is obvious (T=3), with 32 capsomeres per nucleocapsid (180 protein subunits).

Genome

Monopartite, linear, single stranded, positive sense RNA about 4100 to 4500 nucleotides long. The 3' terminus has neither a poly(A) tract nor a tRNA-like structure. The 5' terminus has a genome-linked protein (VPg) which is probably essential for infectivity.

Genus Genomic Organization

There are three or four open reading frames:

N.B. Recent results suggest that all members may actually follow the CfMV pattern of gene expression but this is not represented in most of the sequence files.

Type Member Genomic Organization

It has generally been thought that there are four open reading frames. The sequence L34672 has proved to be rather abnormal compared with other isolates (and other viruses in the genus) so this description is based on the Arkansas isolate (AF055888):
1. 17.2 kDapossible movement protein
2. 106.5 kDa polyprotein, including a serine protease-like domain, the VPg and an RNA-dependent RNA polymerase domain
3. 14.8 kDaunknown function but may be expressed as a frame-shift fusion with the 5'-part of ORF2
4. 28.6 kDacoat protein, expressed from subgenomic RNA of about 1000 nucleotides

N.B. Recent results suggest that all members may actually follow the CfMV pattern of gene expression but this is not yet represented in the sequence files.