Notes on Genus: Ipomovirus
Type member: Sweet potato mild mottle virus
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 white fly transmission. Like all the genera except the genus Bymovirus
, it has a monopartite genome. It's name is derived from Ipomoea
, the generic name of sweet potato, the host of the type member, sweet potato mild mottle virus.
Virions filamentous, not enveloped, usually flexuous, 750-950 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.
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
but shows some variation in detail between members. The genome is translated into a single polyprotein, which is subsequently processed into about ten products, with the coat protein at the C-terminus. Some members of this genus lack the HC-Pro cistron. In some of these cases there appears to be two (divergent) copies of the P1 protein in its place, while in the cassava-infecting members, an additional HAM-1 like protein has been identified between the NIb and coat protein regions. As in other members of the family, an additional small ORF (PIPO) is generated by frameshifting within the P3 cistron.
Type Member Genomic Organization
The genome is translated into a single polyprotein of 390 kDa, from which an estimated ten functional products are produced by proteolytic processing:
|P1 protein|| ||putative protease|| ||83 kDa|
|HC-Pro ||putative helper component protease|| ||51 kDa|
|P3 protein||unknown function || ||34 kDa|
|"6K1"||unknown function || ||5 kDa|
|CI ||Cylindrical inclusion putative helicase|| ||71 kDa|
|"6K2"||unknown function || ||6 kDa|
|VPg||Genome-linked protein || ||20 kDa|
|NIa-Pro||Nuclear Inclusion protease || ||27 kDa|
|NIb||Nuclear Inclusion polymerase || ||57 kDa|
|CP|| ||Coat protein || ||34 kDa|
An additional small ORF (PIPO) is generated by frameshifting within the third cistron (P3).