Virus Family Basics

Hepadnaviruses are characterized by:

Envelope--  spherical, 42nm in diameter, contains cellular lipids, glycoproteins, and a virus-specific surface antigens such as HBsAg.

Icosahedral Capsid-- 27nm core. The core contains contains an antigen (HBcAg), DNA polymerase, and a small, circular, partially double stranded DNA. Capsid is closely surrounded by the viral envelope. T=3 triangulation number.

Viral genome-- Circular, 3.2kb, partially double-stranded DNA containing four overlapping open reading frames.  It has the smallest genome of DNA viruses. One DNA strand, the minus strand has a protein covalently attached to the 5' end. The plus strand is of variable length and is shorter than the negative strand, and has an RNA oligonucleotide at its 5' end.

Picture courtesy of http://www.stanford.edu/group/virus/hepadna/index.html

-strand is outer strand. Shorter +strand is on inside. DR1 and DR2 are repeated elements. Other blacks boxes refer to promoters/enhancers.  Dashed line refers to the variable length of the +strand.

Protein Products include:

• P protein-- Reverse Transcriptase polymerase protein.

• PreC and C (a.k.a HBcAg)-- Core proteins

•  PreS1, PreS2, and S (a.k.a. HBsAg)-- Surface proteins

• X-- A transcriptional activator that might be of importance in HBV-associated cancer that is only present in mammalian hepadnaviruses.

The rest of discussion will be based on Hepatitis B Virus (HBV) as more is known about this virus than other viruses in the Hepadnavirus family.