Notes on Genus: Fabavirus

icosahedra

Type member: Broad bean wilt virus 1

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 scientific name of the host (Vicia faba) of the type member (broad bean wilt virus 1). 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. Although originally included in the genus Comovirus, Fabaviruses are serologically unrelated to members of that genus and are transmitted by aphids (rather than beetles).

Morphology

Virions isometric (icosahedral), not enveloped, of two types but similar in size (about 30 nm in diameter) and appearance. Nucleocapsids appear to be angular.

Virions composed of 25 % nucleic acid (M component), or 35 % nucleic acid (B 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. 3600 nucleotides) into M particles. The 3' terminus of each RNA has a poly(A) tract and the 5' terminus probably has a genome-linked protein (VPg).

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 two coat proteins and a cell-to-cell movement product 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 produces a polyprotein of 206 kDa processed into 5 peptides necessary for replication:
1. 35 kDaProcessing regulator (protease co-factor)
2. 66 kDaNucleotide binding protein with helicase activity
3. 3.1 kDaVPg: genome-linked protein
4. 23 kDa Protease
5. 79 kDa Polymerase
RNA2 produces a polyprotein of 114 kDa processed into 3 functional peptides:
1. 47 kDa Movement protein
2. 44 kDaLarge coat protein
3. 23 kDaSmall coat protein