Transcription of woodchuck hepatitis virus in the chronically infected liver.

The transcription of woodchuck hepatitis virus (WHV) genome was studied in the liver of chronically infected woodchucks by Northern blot, nuclease mapping and primer extension analysis. Two major transcripts, 2.1 and 3.7 kb in length, and several minor transcripts were found in samples which supported active WHV replication. The 2.1-kb RNA represents the major transcript of the S gene, encoding the viral surface antigen (WHsAg) as demonstrated by blot-hybridization experiments. Two transcription initiation sites were localized downstream of the second AUG of the pre-S region, 139 and 152 nucleotides upstream of the translation initiation codon of the S gene. The 3.7-kb transcript, present in an equal amount, is slightly larger than the WHV genome and could be involved in the expression of all viral proteins. The data derived from RNA mapping strongly suggest that this transcript is initiated approximately 70 nucleotides upstream of the C gene, encoding the viral core antigen (WHcAg), and represents the message for WHcAg. It might also serve in the viral replication cycle as a potential template for reverse transcription. All WHV-specific transcripts were found to be processed at a unique site, 20 nucleotides downstream of the polyadenylation signal situated within the core gene. A different set of WHV-specific mRNAs was observed in a woodchuck hepatocellular carcinoma when only integrated forms of WHV DNA could be detected. Two RNA species of 2.3 and 4.6 kb were characterized. The 3.7-kb RNA was absent, reinforcing the hypothesis that this transcript corresponds to the pre-genome.