Hepatitis B virus (HBV)-specific structures found in cytoplasmic extracts of cells producing HBV surface antigen (HBsAg) in vitro.

Two kinds of hepatitis B virus-specific particles are present in cytoplasmic extracts of hepatoma cells synthesizing hepatitis B virus (HBV) surface antigen. One class of particle contains the surface antigen of the virus, is 20S in size and has a buoyant density (in CsCl) of 1.2 g/ml. The second class of particle is a deoxyribonucleoprotein (CNP) with 1.3 g/ml buoyant density (in CsCl) and is 30S in size, the DNA of which contains HBV sequences thus proving virus specificity.