Hepadnaviridae

Template:Taxobox begin Template:Taxobox begin placement virus Template:Taxobox group vii entry Template:Taxobox familia entry Template:Taxobox end placement Template:Taxobox section subdivision Orthohepadnavirus
Avihepadnavirus Template:Taxobox end Hepadnaviruses are the viruses in the family Hepadnaviridae. Hepadnaviruses cause liver infections in humans and animals. There are two genera included here:

• Genus Orthohepadnavirus; type species: Hepatitis B virus
• Genus Avihepadnavirus; type species: Duck hepatitis B virus

Hepadnaviruses have very small genomes of partially double-stranded, partially single stranded non-circular DNA. The genome consists of two uneven strands of DNA of which one is in a negative sense orientation and the other longer strand is in a negative sense orientation. As it is a group 7 virus, replication involves a RNA intermediate. Three main open reading frames are encoded (ORFs) and the virus has four known genes which encode the core protein, the virus polymerase, surface antigens (preS1, preS2 and preS3) and the X protein. The X protein is thought to be non structural; however its function and significance is poorly understood.

Hepadnavirus Replication

They have a peculiar mode of replication; they replicate through an RNA intermediate (which they transcribe back into cDNA using reverse transcriptase). Most hepadanaviruses will only replicate in specific hosts and this makes experiments using in vitro methods very difficult.

The virus binds to specific receptors on cells and the core particle enters the cell cytoplasm. This is then translocated to the nucleus where the partially double stranded DNA is 'repaired' by the cell to form a complete circle of DNA. This then undergoes transcription by the host cell RNA polymerase and the transcript is translated by host cell ribosomes. New virus particles are formed which acquire lipid from the endoplasmic reticulum of the host cell and the genome is packaged within these particles which then bud off from the cell.