Takemitsu Nagahata

An in vitro system for screening anti-hepatitis b virus drugs

A human hepatoblastoma cell line (HB 611) that continuously synthesizes hepatitis B viral (HBV) DNA was grown in the presence of various inhibitors of DNA synthesis, and the DNA from the cells was analyzed by the Southern blotting method to examine selective inhibition of the viral DNA synthesis. Among those that showed selective inhibition, and interferons alpha and beta, acyclovir, and dideoxy cytidine were effective. This system should be useful for screening new antiviral agents against HBV.

Translation of hepatitis B virus DNA polymerase from the internal AUG codon, not from the upstream AUG codon for the core protein

Hepatitis B virus DNA replicates via its own polymerase that also acts as reverse transcriptase (Summers and Mason, 1982). This enzyme is encoded by a 3.5 Kb mRNA transcript covering the whole genome. Since the same transcript also codes for the core protein, and since the core open reading frame (ORF) is located upstream of the pol ORF, it has been suggested that the polymerase is first produced as a core-pol fusion protein that subsequently undergoes cleavage. This is already known to be the case with retrovirus reverse transcriptase, for which a gag-pol fusion protein is made first and the latter protein is liberated by proteolytic cleavage. We investigated this problem using mutants that were modified at the translation initiation codon for the core and precore ORF. Our findings suggested that polymerase translation occurred from the internal AUG codon independently of core protein synthesis, and that obligatory production of the core-pol fusion protein is accordingly unlikely.