Notes on Genus: Ampelovirus
Type member: Grapevine leafroll-associated virus 3
This is one of three genera in the family Closteroviridae
, which are characterised by their very long (950-2000 nm) and very flexuous particles. Viruses in this genus were previously classified in the genus Closterovirus
, but have been separated because of their mealybug transmission and different genome organisation. The name is from the Greek ampelos
meaning grapevine, the plant host of the type member.
Virions filamentous, not enveloped, very flexuous, 950-2000 nm long and 10-13 nm in diameter. There is a distinct virion tail. Symmetry helical, with pitch of 3.4-3.7 nm.
Virions composed of 5% nucleic acid.
Monopartite, linear, single-stranded, positive sense RNA 15,000 to 20,000 nucleotides long. There are sequences with potential hairpin structure near the 3'-end. 3' terminus has no poly(A) tract and the 5' terminus probably has a methylated nucleotide cap.
Genus Genomic Organization
The RNA is translated from up to 12 reading frames. There is a large replicase near the 5'-end and the coat proteins are towards (but not at) the 3'-end.
Type Member Genomic Organization
The RNA is believed to be translated from twelve open reading frames:
|1a ||245 kDa ||replication protein |
|1b || 61 kDa ||polymerase, expressed as a 1a/1b fusion protein|
|2 || 6 kDa ||unknown protein |
|3 || 5 kDa ||unknown protein |
|4 ||59 kDa ||similar to the HSP70 heat-shock proteins which are molecular chaperones|
|5 ||55 kDa ||probably involved in cell-to-cell movement|
|6 ||35 kDa ||Coat protein; assembled into particles as the major virion protein|
|7 ||53 kDa ||Minor coat protein incorporated into the virion tail|
|8 ||21 kDa ||unknown protein |
|9 ||20 kDa ||unknown protein |
|10 ||20 kDa ||unknown protein |
|11 || 4 kDa ||unknown protein |
|12 || 7 kDa ||unknown protein |