title: The hepatitis B virus X-C fusion protein is unlikely to be produced by the mechanism of ribosomal frameshifting.
abstract: A novel hepatitis B viral (HBV) protein of 35-40 kDa, characterized by antibodies and proposed as an X-C fusion protein, was previously described in core particles isolated from HBV-, WHV-, and GSHV-infected livers. The X and C genes are two adjacent genes in all mammalian hepadnaviruses but are not contiguous in WHV and GSHV. After examination of the X and preC/C junction sequences of 10 HBV, 4 WHV, and 1 GSHV, we found that the ORF of preC can be extended 7 more sense codons upstream so that X overlaps with the preC/C gene in all sequences. The number of overlapping base pairs (bp) is varied: 46 bp in HBV, 19 bp in WHV, and 10 bp in GSHV. In this region a conserved A-track was found to be followed by a pair of inverted repeats, suggesting that a ribosomal frameshift may occur for X-C fusion protein production. To assess this possibility, we have used an in vitro transcription and translation coupling system to identify X-C protein production. Two recombinant SP6 plasmids were used. One contained a full length of the X and preC/C gene of wild-type HBV-DNA and the other fused the X-preC/C gene by inserting a 10-bp HindIII linker at the junction of the X-preC/C region. No X-C fusion protein was detected from the wild-type plasmid. In contrast a large amount of X-C fusion protein was produced from the linker-inserted clone. It appears, therefore, that the X-C fusion protein is unlikely to be produced via the mechanism of ribosomal frameshifting.
authors.affiliation: Graduate Institute of Microbiology and Immunology, National Yang-Ming Medical College, Taipei Taiwan, Republic of China.
authors.forename: S J
authors.initials: SJ
authors.lastname: Lo
authors.forename: L R
authors.initials: LR
authors.lastname: You
authors.forename: Y H
authors.initials: YH
authors.lastname: Lee
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D004279:DNA, Viral / Q000737:chemistry; D016368:Frameshift Mutation; D005814:Genes, Viral; D006515:Hepatitis B virus / Q000235:genetics*; D008969:Molecular Sequence Data; D016366:Open Reading Frames; D012091:Repetitive Sequences, Nucleic Acid; D012270:Ribosomes / Q000502:physiology*; D012689:Sequence Homology, Nucleic Acid; D015534:Trans-Activators / Q000235:genetics*; D014760:Viral Fusion Proteins / Q000235:genetics*; D054334:Viral Regulatory and Accessory Proteins
chemical_list: D004279:DNA, Viral; D015534:Trans-Activators; D014760:Viral Fusion Proteins; D054334:Viral Regulatory and Accessory Proteins; C066051:X-C fusion protein, Hepatitis B virus; C057628:hepatitis B virus X protein