Notes on Genus: Alphamesonivirus
Type member: Alphamesonivirus 1
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
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