Notes on Genus: Comovirus

icosahedra

Type member: Cowpea 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

This is one of 3 genera in the subfamily Comovirinae of the plant picornavirus family Secoviridae and derives its name from the type member, cowpea mosaic virus. In common with other genera in the subfamily, its members are characterised by their bipartite genome encapsidated in icosahedral particles with each genome segment producing a polyprotein. Unlike the other genera, members can be transmitted by beetles and have two coat proteins of different sizes

Morphology

Virions isometric (icosahedral), not enveloped, of two types but similar in size (about 28 nm in diameter) and appearance. 32 capsomeres per nucleocapsid (12 pentamers plus 20 trimers). Incomplete virus particles (empty capsids) are often present (T component).

Genome

Bipartite, linear, single stranded, positive sense RNA. The genome segments are encapsidated separately into different types of particles: RNA1 (c. 6000 nucleotides) into B and RNA2 (c. 3500 nucleotides) into M particles. The 3' terminus of each RNA has a poly(A) tract and the 5' terminus has a genome-linked protein (VPg), covalently bound through serine.

Genus Genomic Organization

Each RNA is translated into a polyprotein, which is then processed by a series of steps into functional proteins: RNA1 encodes proteins necessary for replication while the (two) coat proteins and products involved in cell-to-cell movement are encoded on RNA2.

Type Member Genomic Organization

Each RNA is translated into a polyprotein, which is then processed by a series of steps into functional proteins:

RNA1 (5889 nucleotides) produces a polyprotein of 202 kDa processed into 5 peptides:
1. 32 kDaProcessing regulator (protease co-factor)
2. 58 kDaNucleotide binding protein with helicase activity
3. 4 kDaVPg: genome linked protein
4. 24 kDaProtease produced from 110 kDa intermediate
5. 87 kDaPolymerase produced from 110 kDa intermediate
RNA2 (3481 nucleotides) produces a polyprotein of 105 or 95 kDa processed into 4 functional peptides:
1. 58 kDa Movement protein (cell-to-cell-movement)
2. 48 kDacell-to-cell-movement protein, derived from 58 kDa product
3. 37 kDa Large coat protein
4. 23 kDaSmall coat protein