Notes on Genus: Blosnavirus

icosahedra
icosahedra

Type member: Blotched snakehead virus

Contents

General Description

The genus Blosnavirus (from the type member Blotched snakehead virus) is one of four genera in the family Birnaviridae and contains viruses isolated from fish. Compared with other genera, there is an extra protein cleaved from the polyprotein on segment A and the sequences are only distantly related.

Morphology

Virions isometric (icosahedral), not enveloped, 60 nm in diameter, made of 260 units trimeric subunits.

Genome

Bipartite double-stranded RNA of about 3.4 and 2.8 kb, probably with a genome-linked protein (VPg) at the 5'-terminus and no 3'-polyA tail.

Genus Genomic Organization

Each segment encodes a large polyprotein that it is subsequently processed into the functional products and there is an additional, smaller ORF on the larger (A) segment. The two capsid proteins and a non-structural protein are encoded on segment A and an RNA-dependent RNA polymerase on segment B.

Type Member Genomic Organization

Segment A (3.4 kb) encodes:
  • ORF1: VP5, 15 kDa protein of unknown function
  • ORF2: 115 kDa, Polyprotein that is subsequently processed into:
    • VP2, 52 kDa major outer capsid protein precursor that undergoes further truncation and cleavage
    • X protein, 8 kDa of unknown function
    • VP4, 25 kDa protease
    • VP3, 31 kDa internal capsid protein
Segment B (2.8 kb) encodes a single 97 kDa protein (VP1) from ORF3 that is an RNA-dependent RNA polymerase.