Notes on Genus: Bymovirus

flexuous filaments

Type member: Barley yellow mosaic virus

General Description

This is one of the genera in the family Potyviridae. Bymoviruses (barley yellow mosaic virus group) are distinguished from other Potyviridae by having bipartite genomes and by 'fungal' transmission. The vector (or putative vector) of all members is a common root-infecting parasite, Polymyxa graminis Ledingham, which is classified in the Plasmodiophorales. Polymyxa graminis and other plasmodiophorid 'fungi' also transmit Furoviruses.

Morphology

Virions filamentous, not enveloped. Of two lengths: 500-600 and 200-300 nm long x 12-15 nm in diameter. Symmetry helical. Pitch of helix 3.4 nm.

Virions composed of 5 % nucleic acid; 95 % protein.

Genome

Linear, single stranded positive sense RNA. Genome bipartite with total genome 10000-12000 nucleotides long. 3' terminus has a poly(A) tract. 5' terminus has a genome-linked protein (VPg).

Genus Genomic Organization

Each RNA is translated into a polyprotein, which is subsequently processed into a number of structural and non-structural proteins. Many of these have sufficient homology to Potyviruses for functions to be tentatively assigned.

RNA1 is believed to produce 8 peptides:
P3 protein	30-40 kDa	unknown function
"6K1"	7-8 kDa	unknown function
CI	70-75 kDa	cylindrical inclusion protein with helicase activity and possibly involved in cell to cell movement
"6K2"	7-14 kDa	unknown function
VPg	20-22 kDa	putative genome-linked protein
NIa-Pro	24-25 kDa	Serine-like protease (NIa-Pro).
NIb	59-61 kDa	homologous to potyvirus Nuclear Inclusion polymerase
CP	25-35 kDa	Coat protein
RNA2 produces 2 peptides:
P1 protein	25-30 kDa	including a protease domain similar to that of the potyvirus HC-Pro
P2 protein	70-75 kDa	involved in fungus transmission. Some laboratory isolates have deletions in this region

An additional small ORF (PIPO) is generated by frameshifting within the first cistron of RNA1 (P3).

Type Member Genomic Organization

Each RNA is translated into a polyprotein, which is subsequently processed into a number of structural and non-structural proteins:

RNA1 is believed to produce 8 peptides:
P3 protein	38 kDa	unknown function
"6K1"	7 kDa	unknown function
CI	74 kDa	cylindrical inclusion protein with helicase activity and possibly involved in cell to cell movement
"6K2"	14 kDa	unknown function
VPg	22 kDa	putative genome-linked protein
NIa-Pro	25 kDa	Serine-like protease (NIa-Pro).
NIb	60 kDa	homologous to potyvirus Nuclear Inclusion polymerase
CP	32 kDa	Coat protein
RNA2 produces 2 peptides:
P1 protein	28 kDa	including a protease domain similar to that of the potyvirus HC-Pro
P2 protein	70 kDa	involved in fungus transmission