Notes on Genus: Avibirnavirus

icosahedra
icosahedra

Type member: Infectious bursal disease virus

Contents

General Description

The genus Avibirnavirus (from the Latin avis = bird) is one of four genera in the family Birnaviridae and contains viruses isolated from birds.

Morphology

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

Genome

Bipartite double-stranded RNA of about 3.2 and 2.8 kb, each 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 (3.2 kb) encodes:
  • ORF1: 16-17 kDa, non-structural protein VP5 of unknown function
  • ORF2: 106-110 kDa, Polyprotein that is subsequently processed into:
    • VP2, major outer capsid protein precursor that undergoes further truncation and cleavage
    • VP4, protease
    • VP3, internal capsid protein
Segment B (2.8 kb) encodes a single 94-97 kDa protein (VP1) from ORF3 that is an RNA-dependent RNA polymerase.