DNA-protein complex from hepatitis B virus

Hepatitis B virus (HBV) DNA labelled with [3H] or [alpha-32P]dTTP in vitro was isolated from Dane particles by CsCl-guanidine hydrochloride density gradient centrifugation. Virtually all HBV DNA extracted as above contained a knob on the double-stranded region visible by electron microscopy. Proteinase K removes the know from HBV DNA. The HBV DNA-protein complex was efficiently bound to nitrocellulose membrane filters. When the radioactively labelled HBV DNA-protein complex was digested with restriction endonuclease Hae III or Hind II and subjected to polyacrylamide gel electrophoresis, some radioactivity did not enter the gel. Restriction endonuclease fragments did not remain on the top of the gel after proteinase K treatment and no new band was detected. The possible role of the knob protein in the replication of HBV DNA is discussed.