Notes on Genus: Tymovirus
Type member: Turnip yellow mosaic virus
The genus Tymovirus
saic virus group) is one of three genera in the family Tymoviridae
, all of which have a similar 30 nm icosahedral particles and which are related in phylogenetic analysis. Members differ from those of the other genera in having a single coat protein and by their sap and beetle transmission. Members of the genus Marafivirus
have two coat proteins and are transmitted only by leafhoppers, while those of the genus Maculavirus
have larger genomes, are phloem limited and have no known vectors.
Virions isometric (icosahedral; T=3), not enveloped, 30 nm in diameter. 32 capsomeres per nucleocapsid (12 pentamers and 20 hexamers). Incomplete virus particles (empty capsids) are also present.
Virions often contain polyamines (several hundred molecules of spermine and spermidine).
Monopartite, linear, single stranded, positive sense RNA c.
6300 nucleotides long. The 3'-terminus has a tRNA-like structure accepting valine (in the type member). The 5' terminus has a methylated nucleotide cap.
Genus Genomic Organization
The RNA encodes three proteins, which in the well-characterised members are:
|1. ||69-85 kDa ||Movement protein (cell-to-cell movement), overlapping with ORF2|
|2. ||205-210 kDa|| Replication protein |
|3. ||c. 20 kDa|| Coat protein, expressed from a 3'-coterminal subgenomic mRNA |
Type Member Genomic Organization
The RNA encodes three proteins:
| 1. ||69 kDa || Movement protein|
|2. ||206 kDa||Replication protein with nucleotide binding and RNA polymerase functions. It may be autocatalytically proteolysed in vitro into products of 150 and 70 kDa|
|3. ||20 kDa||Coat protein, expressed from a 3'-coterminal subgenomic mRNA of c. 800 nucleotides|