Notes on Genus: Tungrovirus
Type member: Rice tungro bacilliform virus
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
Virions bacilliform, not enveloped, 30-35 nm in diameter and 110-400 nm in length.
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 |