Notes on Genus: Tobamovirus
Type member: Tobacco mosaic virus
The genus Tobamovirus
saic virus group) is the only genus of plant viruses with rigid rod shaped particles and a monopartite genome. Members of the genus are transmitted by sap and sometimes by seed.
Virions rod-shaped, not enveloped, usually straight and with a distinct central canal. Mostly 300 nm long and18 nm in diameter. Symmetry helical with pitch of 2.3 nm.
Virions composed of 5 % nucleic and 95 % protein.
Monopartite, linear, single stranded, positive sense RNA about 6400 nucleotides long. The 3'-terminus has a tRNA-like structure (which accepts histidine). The 5' terminus has a methylated nucleotide cap with the sequence m7
Genus Genomic Organization
The genome encodes at least four proteins, two of which (126-129 and 183-187 kDa) are involved in virus replication. These are in the 5' half of the genome and the larger one is produced by readthrough of the termination codon of the first gene. The other two, a movement protein (28-31 kDa) and the coat protein (17-18 kDa) are expressed from separate subgenomic mRNAs.
Type Member Genomic Organization
The genome encodes at least four proteins:
|1. ||126 kDa ||Relication protein with methyl transferase and helicase domains|
|2. || 183 kDa ||Polymerase readthrough incorporating RdRp domain|
|3. ||30 kDa|| Movement protein, expressed from 3'-coterminal subgenomic mRNA I2 (1500 nucleotides)|
|4. || 17 kDa||Coat protein, expressed from 3'-coterminal subgenomic mRNA (692 nucleotides)|