Avibirnavirus (taxid:39751)

VIRION

Non enveloped, single-shelled T=13 icosahedral symmetry capsid of about 70 nm in diameter, composed of 260 trimers of VP2 that form spikes projecting radially from the capsid. The peptides derived from pre-VP2 C-terminal cleavages remain associated within virion. VP3 forms a ribonucleoprotein complex with the genomic RNA. Minor amounts of VP1 are also incorporated in the virion.

GENOME

Segmented linear dsRNA genome: 2 segments (A,B) encode for 5 proteins. VP1 is found in a free form and covalently attached at the 5' genomic RNA end (VPg). Segments size is about 2.9-3 kb. Genome total size is about 6 kb.

GENE EXPRESSION

Genomic segment A encodes for a structural polyprotein which is matured in cis by VP4. It also encodes an alternative ORF (VP5) translated possibly by leaky scanning.
Genomic segment B encodes for VP1.

ENZYMES

• Polyprotein protease (Peptidase S50) [Q82635]
• RNA-dependent RNA polymerase [Q82630]

REPLICATION

CYTOPLASMIC

1. Virus penetrates into the cytoplasm.
2. Transcription of the dsRNA genome by viral polymerase occurs inside the virion, so that dsRNA is never exposed to the cytoplasm. This plus-strand transcript is used as template for translation.
3. (+)RNAs are encapsidated in virion particle, inside which they are transcribed to give RNA (-) molecules with which they become base-paired to produce dsRNA genomes.
4. Mature virions are released by budding.

Host-virus interaction

Host transcription modulation

Apoptosis modulation

Infectious bursal disease virus (IBDV) destroys its target cells, the B-lymphocytes precursors, by inducing caspases activation and apoptosis. VP5 seems to be the major apoptosis inducer through its interaction with the voltage-dependent anion channel 2 (VDAC2) .