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Virus classification
Group: Group IV ((+)ssRNA)
Family: Unassigned
Genus: Sobemovirus

Southern cowpea mosaic virus

The Sobemovirus is a genus of a virus with no family.


The virion capsids are non-enveloped, round and isometric, with a diameter of 25–33 nm.

The genome is a single piece of linear, positive-sense, single-stranded RNA, 4100–5700 nucleotides in length.[1] The genome encodes five open reading frames: ORF1, ORFs 2a and 2b, ORF3 and ORFx.[2]

ORF1 encodes P1 which plays a role in suppression of silencing and virus movement.

ORFs 2a and 2b encode the replicational polyproteins P2a and P2ab. Translation of ORF2a from the genomic RNA is dependent on a leaky scanning mechanism.

ORF3 encodes the coat protein.

ORFx is conserved in all sobemoviruses. It overlaps the 5' end of ORF2a in the +2 reading frame and also extends some distance upstream of ORF2a. It lacks an AUG initiation codon and its expression is predicted to depend on low level initiation at near-cognate non-AUG codons, such as CUG, by a proportion of the ribosomes that are scanning the region between the ORF1 and ORF2a initiation codons. Its function is unknown but it appears to be essential for infection.


The Southern cowpea mosaic virus is the type species.


  1. ^ Index of Viruses—Sobemovirus (2006). In: ICTVdB—The Universal Virus Database, version 4. Büchen-Osmond, C (Ed), Columbia University, New York, USA.
  2. ^ Ling R, Pate AE, Carr JP, Firth AE. An essential fifth coding ORF in the sobemoviruses. Virology pii: S0042-6822(13)00314-0. doi: 10.1016/j.virol.2013.05.033

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