Notes on Genus: Alphanecrovirus

icosahedra

Type member: Tobacco necrosis virus A

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

Necroviruses, (named from tobacco necrosis virus) are members of the family Tombusviridae. Until 2013, these were included in a single genus but the high level of sequence diversity in the polymerase, and (two) movement protein sequences led to the genus being divided into 2 genera. Like other members of the family, necroviruses have icosahedral particles and small, monopartite ss RNA genomes. In common with the genera Machlomovirus and Panicovirus, necroviruses have a small (27-30 kDa) coat protein but the necrovirus genome is smaller (<4 kb). In natural infections necroviruses are typically restricted to roots and transmitted by the fungus Olpidium brassicae.

Morphology

Virions isometric (icosahedral), 28nm in diameter. 32 capsomeres per nucleocapsid.

Genome

Monopartite, linear, single stranded positive sense RNA about 4000 nucleotides long. 3' terminus has no poly(A) tract. 5' terminus has a ppApGpUp...sequence.

Genus Genomic Organization

There are 5 (or 6) ORFs. ORFs1 and 2 (a readthrough of 1) are believed to be a polymerase. The small ORFs 3 and 4 are probably translated from the larger of two subgenomic RNAs and the coat protein (ORF5) from a smaller subgenomic.

Type Member Genomic Organization

The RNA is translated by means of several open reading frames (ORFs) into 6 products:

1	23 kDa	Replication protein
2	82 kDa	Polymerase readthrough
3	8 kDa	Movement protein
4	6 kDa	Putative movement protein
5	30 kDa	Coat protein
6	7 kDa	unknown function