Notes on Genus: Tungrovirus

bacilliform

Type member: Rice tungro bacilliform 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 Caulimoviridae, which are distinctive amongst plant viruses in having double-stranded DNA. Members of this genus are those with bacilliform, rather than isometric, particles and with 4 open reading frames in the genome. The single member of the genus was previously classified in the Badnavirus genus, but this now only includes those viruses with 3 open reading frames. The name is derived from the type member, Rice tungro bacilliform virus.

Morphology

Virions bacilliform, not enveloped, 30-35 nm in diameter and 110-400 nm in length.

Genome

Monopartite, open circular, double stranded DNA of c.8000 base pairs with a single-strand discontinuity at one site in each strand.

Genus Genomic Organization

The genome has direct terminal repeats, reiterated internally in inverted form and is translated from 4 open reading frames (ORFs) on the same DNA strand. The largest of the ORFs is probably a polyprotein, subsequently processed into several functional products.

Type Member Genomic Organization

There are 4 open reading frames on the same DNA strand:
ORF1 26 kDa unknown function
ORF2 12 kDa DNA binding protein
ORF3 194 kDa polyprotein which is cleaved by aspartic proteinase to give a putative movement protein, a coat protein, a proteinase, and a replicase which has a reverse transcriptase activity, a DNA polymerase DNA dependant activity, and a RNAse H activity
ORF4 46 kDa similar to the caulimovirus transactivator factor inclusion body protein