Notes on Genus: Entomobirnavirus

icosahedra
icosahedra

Type member: Drosophila X virus

Contents

General Description

The genus Entomobirnavirus (from the Greek entomon = insect) is one of four genera in the family Birnaviridae and contains viruses isolated from insects.

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 3.2 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 (3.4 kb) encodes:
  • ORF1: 27 kDa, VP5 protein of unknown function
  • ORF2: 114 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 (3.2 kb) encodes a single 113 kDa protein (VP1) from ORF3 that is an RNA-dependent RNA polymerase.