Notes on Genus: Topocuvirus

twinned icosahedra
twinned icosahedra

Type member: Tomato pseudo-curly top virus


General Description

This is one of 7 genera in the family Geminiviridae. It differs from the genus Begomovirus in having a monopartite genome and treehopper vectors. It differs from the other monopartite genera because the genome encodes 6 proteins and its members infect dicotyledonous plants. The genus Mastrevirus has a slightly smaller genome, encoding 3 or 4 proteins and most members infect graminaceous plants, while the genus Curtovirus is characterised by a genome encoding 7 proteins.


Virions are geminate (twinned) icosahedra, not enveloped, 38 nm long and 22 nm in diameter. 22 capsomeres per nucleocapsid.


Monopartite, closed circular, single stranded DNA, about 2850 nucleotides long.

Genus Genomic Organization

There are two open reading frames (ORFs) in the positive (virion) sense and four in the negative (complementary) sense.

Type Member Genomic Organization

V1+27 kDa Coat protein
V2+11 kDa Movement protein
C1-40 kDa Replicase A
C2-18 kDa Replicase B
C3-16 kDa similar to the replication enhancer protein of begomoviruses
C4-9 kDa initiates cell division; symptom determinant