Notes on Genus: Brambyvirus

flexuous filaments

Type member: Blackberry virus Y

General Description

This is one of the genera in the family Potyviridae. Like the other genera, it is characterised by its flexuous filamentous particles, inclusion bodies in infected plant cells and by having a polyprotein genome strategy. It differs from most of the other genera in having a very large P1 protein containing an AlkB domain. The vector is not known. Like all the genera except the genus Bymovirus, it has a monopartite genome. Its name is derived from bramble, one of the common names for the host of the type member, Blackberry virus Y.

Morphology

Virions filamentous, not enveloped, usually flexuous, about 800 nm long and 12-15 nm in diameter. Symmetry helical with a pitch of 3.4 nm

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

Genome

Monopartite, linear, single stranded, positive sense RNA, about 11,000 nucleotides long. The 3' terminus has a poly(A) tract and the 5' terminus has a genome-linked protein (VPg).

Genus Genomic Organization

Genome organisation is similar to that of other members of the family Potyviridae. The genome is translated into a single polyprotein, which is subsequently processed into about ten products, with the coat protein at the C-terminus. An additional small ORF (PIPO) is generated by frameshifting within the third cistron (P3).

Type Member Genomic Organization

The genome is translated into a single polyprotein of 394 kDa, from which an estimated ten functional products are produced by proteolytic processing:

P1 protein	putative protease	84 kDa
HC-Pro	putative helper component protease	37 kDa
P3 protein	unknown function	41 kDa
"6K1"	unknown function	6 kDa
CI	Cylindrical inclusion putative helicase	71 kDa
"6K2"	unknown function	6 kDa
VPg	Genome-linked protein	22 kDa
NIa-Pro	Nuclear Inclusion protease	26 kDa
NIb	Nuclear Inclusion polymerase	61 kDa
CP	Coat protein	41 kDa

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