Notes on Genus: Alphamesonivirus

enveloped spheres
enveloped spheres

Type member: Alphamesonivirus 1


General Description

The genus Alphamesonivirus is currently the only genus in the family Mesoniviridae, and contains insect-infecting nidoviruses. The genus (and family) name reflects the fact that the genomes are intermediate (Greek, meso = medium) in size between those of the small nidoviruses in the family Arteriviridae and those of the large nidoviruses in the families Coronaviridae and Roniviridae.


Virions are enveloped spheres about 60-80 nm in diameter.


Monopartite, linear single-stranded RNA, about 20 kb long with a polyA tail at the 3'-terminus.

Genus Genomic Organization

Two large, overlapping ORFs at the 5'-end of the genome encode the major non-structural proteins and are expressed as a fusion protein by ribosomal frameshift. Downstream are at least 4 other genes, mostly or entirely encoding structural proteins, and these are probably expressed from a 3'-coterminal nested set of subgenomic RNAs.

Type Member Genomic Organization

The RNA of 20.2 kb is translated into the following products:
  • Replication protein 1a of 228 kDa
  • Polymerase 1b, expressed as a 588 kDa fusion protein with 1a by ribosomal frameshift
  • Spike protein 2a of 103 kDa
  • Nucleocapsid 2b or 24 kDa
  • Small glycoprotein ORF3 of 17 kDa
  • Small glycoprotein ORF4 of 14 kDa