Notes on Genus: Luteovirus

icosahedra

Type member: Barley yellow dwarf virus-PAV

Contents

• Members of this Genus
• General Description
• Morphology
• Electron Micrograph
• Genome
• Genus Genomic Organization
• Genome Map
• Type Member Genomic Organization
• All Known Sequences
• Curated Sequences

General Description

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.

Morphology

Virions are isometric (icosahedral), not enveloped, 25-30 nm in diameter, with 32 capsomeres per nucleocapsid. They contain 28 % nucleic acid.

Genome

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, Dianthovirus and Carmovirus, 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.