title: Novel short transcripts of hepatitis B virus X gene derived from intragenic promoter.
abstract: The hepatitis B virus X gene encodes a transcriptional trans-activator that appears essential for viral replication in the infected liver. It has been shown by others that at least two X protein products, initiating at different in-frame ATG codons within the X open reading frame, are necessary for full trans-activating function. Yet, previous studies have demonstrated only a full-length X gene transcript that extends 5' of the first ATG codon in the X open reading frame. In this communication, we present evidence for the existence of shorter X gene transcripts, whose heterogeneous 5' ends straddle the second ATG codon of the X open reading frame. These transcripts are not degradation products of the full-length X gene transcripts but rather arise from an independent promoter. Furthermore, immunofluorescence and functional analyses reveal that active X proteins are translated from these transcripts. Therefore, there appears to be a previously undescribed promoter embedded within the X open reading frame that can give rise to functionally important transcripts.
authors.affiliation: Department of Pathology, University of California School of Medicine, San Francisco 94143-0506.
authors.forename: Y W
authors.initials: YW
authors.lastname: Zheng
authors.forename: J
authors.initials: J
authors.lastname: Riegler
authors.forename: J
authors.initials: J
authors.lastname: Wu
authors.forename: T S
authors.initials: TS
authors.lastname: Yen
mesh_terms: D001483:Base Sequence; D006528:Carcinoma, Hepatocellular; D002460:Cell Line; D017931:DNA Primers; D015870:Gene Expression; D005814:Genes, Viral; D006511:Hepatitis B Antigens / Q000096:biosynthesis; D006515:Hepatitis B virus / Q000235:genetics* / Q000378:metabolism*; D006801:Humans; D007438:Introns; D008099:Liver; D008113:Liver Neoplasms; D008969:Molecular Sequence Data; D016366:Open Reading Frames; D010957:Plasmids; D016133:Polymerase Chain Reaction; D011401:Promoter Regions, Genetic; D015183:Restriction Mapping; D015534:Trans-Activators / Q000096:biosynthesis* / Q000235:genetics; D014158:Transcription, Genetic; D015533:Transcriptional Activation; D014407:Tumor Cells, Cultured; D054334:Viral Regulatory and Accessory Proteins
chemical_list: D017931:DNA Primers; D006511:Hepatitis B Antigens; D015534:Trans-Activators; D054334:Viral Regulatory and Accessory Proteins; C057628:hepatitis B virus X protein