Notes on Genus: Luteovirus
Type member: Barley yellow dwarf virus-PAV
The genus Luteovirus
, one of three genera in the family Luteoviridae
, is distinctive for its isometric particles of 25-30 nm diameter, monopartite genome and persistent, aphid transmission. The genus has recently been split and its members reclassified in the new family Luteoviridae
. This genus contains those species that have two ORFs upstream of the coat protein, the second of which is a polymerase expressed as a fusion protein by translational frameshift of ORF1. The genus Polerovirus
now contains those species which have three ORFs upstream of the coat protein gene. The name is from the Latin luteus
, meaning yellow, because of the yellowing symptoms usually produced in infected hosts.
Virions are isometric (icosahedral), not enveloped, 25-30 nm in diameter, with 32 capsomeres per nucleocapsid. They contain 28 % nucleic acid.
Monopartite, linear, single stranded, positive sense RNA 5300-5700 nucleotides long. The 3' terminus has neither a poly (A) tract nor a tRNA-like structure. There is no genome-linked protein (VPg) at the 5'-terminus.
Genus Genomic Organization
Members have two 5'-ORFs with some sequence similarity to the genera Umbravirus
, the second of which is an RNA-dependent RNA polymerase and which may be expressed as a fusion protein with ORF1 by translational frameshift. The remaining (3'-) ORFs are expressed from one or two subgenomic RNAs. These ORFs are:
- coat protein
- coat protein readthrough involved in aphid transmission and possibly cell-to-cell movement
- Movement protein overlapping the coat protein in a different reading frame
- a possible small ORF downstream of the coat protein readthrough, expressed from a second subgenomic RNA.
Type Member Genomic Organization
Six open reading frames have been identified in most isolates:
|ORF1 ||39 kDa||Replication protein|
|ORF2 ||60 kDa ||Polymerase, expressed as a 99 kDa fusion protein (with the 39 kDa protein) by translational frameshift|
|ORF3 ||22 kDa||Coat protein, expressed from subgenomic RNA1 (3000 nucleotides)|
|ORF4 ||17 kDa||putative movement protein, expressed from subgenomic RNA1 (3000 nucleotides)|
|ORF5 ||72 kDa||Coat protein readthrough expressed from subgenomic RNA1 (3000 nucleotides)and involved in aphid transmission|
|ORF6 || 4.1-6.6 kDa||unknown function, expressed from subgenomic RNA2 (800 nucleotides)|
These ORFs are numbered to be consistent with other members of the family Luteoviridae