Avihepadnavirus

VIRION

Enveloped, spherical. Diameter from about 42nm. Icosahedric capsid with a T=4 symmetry.

GENOME

Partially dsDNA circular genome, about 3.2 kb in size. Encodes for 7 proteins.

GENE EXPRESSION

Enzymes: Reverse-transcriptase, RNAse H

REPLICATION

NUCLEO-CYTOPLASMIC

1. Virus attaches to host receptors through major surface antigen and enters the cell by an unknown mechanism.
2. Relaxed circular DNA (RC-DNA) and capsid are transported via microtubules to the nucleus where DNA is released through the nuclear pore, and repaired to form covalently closed circular DNA (cccDNA).
3. Transcription by RNA polymerase II of the pregenomic RNA (pgRNA) and subgenomic mRNAs, inducing synthesis of all the viral proteins.
4. pgRNA is encapsidated, together with the P protein, and reverse-transcribed inside the nucleocapsid in (-)DNA covalently linked to P protein.
5. (+)DNA synthesis from the (-)DNA template generates new RC-DNA.
6. Transport to the nucleus of new RC-DNA leads to cccDNA amplification; alternatively, the RC-DNA containing nucleocapsids are enveloped at the ER, and new virions are released by exocytosis.