Notes on Genus: Orthohepadnavirus

enveloped spheres or pleomorphic

Type member: Hepatitis B virus

Contents

Members of this Genus
General Description
Morphology
Electron Micrograph
Genome
Genus Genomic Organization
Genome Map
Type Member Genomic Organization
Curated Sequences

General Description

This is one of two genera in the family Hepadnaviridae and consists of those viruses that infect mammals, causing primary liver cancer.

Morphology

Virions enveloped, spherical or pleomorphic, 40-45 nm in diameter.

Genome

Monopartite, circular DNA 3.0-3.3 kb long. The genome is partially double-stranded with a full-length negative sense strand and a positive strand of variable length. The circular configuration is achieved by base-pairing between the overlapping 5'-ends of the two strands.

Genus Genomic Organization

There are four major overlapping ORFs in the same orientation. The largest (P) encodes the polymerase. The env or surface gene (S) can be expressed in different lengths to form the 3 surface proteins. The precore/core (preC/C) gene yields two distinct products and the X gene encodes a transcriptional activator.

Type Member Genomic Organization

The genome of 3.2 kbp is translated from four major overlapping ORFs in the same orientation:
  1. Polymerase (P) of 94.6 kDa
  2. The env or surface gene (S) is expressed in different lengths to form the 3 surface proteins. The small protein (S) is 25.4 kDa, the medium protein (M, 31.1 kDa) also contains the pre-S2 region and the large protein (L, 43.7 kDa) contains both the pre-S1 and pre-S2 regions.
  3. The precore/core (preC/C) gene yields two distinct products. The core protein (21.1 kDa) forms the virion shell while the longer product (precore protein, 24.3 kDa) is targeted to the cell's secretory process and is expressed as the "e antigen".
  4. The X gene encodes a transcriptional activator of 16.5 kDa.