Notes on Genus: Tungrovirus
bacilliform
Type member: Rice tungro bacilliform virus
Contents
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 |
