Notes on Genus: Comovirus
Type member: Cowpea mosaic virus
This is one of 3 genera in the subfamily Comovirinae
of the plant picornavirus family Secoviridae
and derives its name from the type member, co
saic 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
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).
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 kDa||Processing regulator (protease co-factor)|
|2. ||58 kDa||Nucleotide binding protein with helicase activity|
|3. ||4 kDa||VPg: genome linked protein|
|4. ||24 kDa||Protease produced from 110 kDa intermediate|
|5. || 87 kDa||Polymerase 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 kDa||cell-to-cell-movement protein, derived from 58 kDa product|
|3. ||37 kDa ||Large coat protein|
|4. ||23 kDa||Small coat protein|