Notes on Genus: Curtovirus

twinned icosahedra

Type member: Beet curly top virus

Contents

• Members of this Genus
• General Description
• Morphology
• Electron Micrograph
• Genome
• Genus Genomic Organization
• Genome Map
• Type Member Genomic Organization
• All Known Sequences
• Curated Sequences

General Description

This is one of 7 genera in the family Geminiviridae. It is also known as Geminivirus Subgroup II or the beet curly top virus group. It differs from the genus Begomovirus in leafhopper or treehopper transmission and in having a monopartite genome. It differs from the other monopartite genera because the genome encodes 7 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 Topocuvirus is characterised by a genome encoding 6 proteins.

Morphology

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

Genome

Monopartite, closed circular, single stranded DNA, 2900-3100 nucleotides long.

Genus Genomic Organization

In most members of the genus there are three open reading frames (ORFs) in the positive (virion) sense and four in the negative (complementary) sense:

ORF	sense	product
V1	+	29-30 kDa	coat protein
V2	+	12-15 kDa	ss/dsDNA regulator
V3	+	10 kDa	movement protein
C1	-	39-44 kDa	replication protein
C2	-	16-20 kDa	unknown function
C3	-	16 kDa	similar to the replication enhancer protein of begomoviruses
C4	-	9-13 kDa	initiates cell division; symptom determinant

The sequence of HrTV lacks C3 and one of the sequences of BSCTV has a fourth ORF in the positive sense.

Type Member Genomic Organization

Examination of the type member sequence (about 3000nt) in the light of those for other members of the genus suggests that there are three open reading frames (ORFs) in the positive (virion) sense and four in the negative (complementary) sense:

ORF	sense	product
V1	+	29.6 kDa	coat protein
V2	+	13.1 kDa	ss/ds DNA regulator
V3	+	10.0 kDa	movement protein
C1	-	44.0 kDa	replication protein
C2	-	20.0 kDa	unknown function
C3	-	16.1 kDa	putative replication enhancer protein
C4	-	9.7 kDa	initiates cell division; symptom determinant