title: Translational regulation of hepatitis B virus polymerase gene by termination-reinitiation of an upstream minicistron in a length-dependent manner.
abstract: Hepatitis B virus (HBV) polymerase (P) gene is translated from the bicistronic pregenomic RNA with the core (C) gene in the first cistron. The P ORF is preceded by the C AUG and three AUG codons within the C region, where a minicistron of 7 amino acids can potentially be translated. Our results indicate that the efficiency of the P gene translation initiation was about 10% of that of the C gene when both genes were fused in-frame to a lacZ reporter in an mRNA similar in structure to the pregenomic RNA. By mutational analysis, about 74% of the translation initiation of HBV P gene was shown to be by ribosomes that reinitiated after terminating translation of this minicistron, while the rest was by two mechanisms: one by ribosomes leaky scanning through every upstream AUG and the other by ribosomal backwards scanning to the P AUG after finishing the translation of the C gene. The efficiency of termination-reinitiation depended on the size of the minicistron, i.e. the reinitiation efficiency decreased about 50% when the size increased from 24 nt to 57 nt. When a 44 nt HBV sequence comprising the minicistron was inserted at the 5' untranslated region of the cat gene, CAT expression was regulated in a similar way to that of the HBV P gene. Moreover, when transfection occurred with an HBV expression plasmid containing an inactivated minicistron, production of virus-like particles dropped to about one-third of the wild-type level, suggesting that the termination-reinitiation mechanism is indeed important for HBV P gene expression.
authors.affiliation: Institutes of Microbiology & Immunology, National Yang-Ming University, Taipei, Taiwan, Republic of China.
authors.forename: W L
authors.initials: WL
authors.lastname: Hwang
authors.forename: T S
authors.initials: TS
authors.lastname: Su
mesh_terms: D000595:Amino Acid Sequence; D019677:Artificial Gene Fusion; D001483:Base Sequence; D002460:Cell Line; D015967:Gene Expression Regulation, Viral; D015684:Gene Products, pol / Q000235:genetics*; D005796:Genes; D017930:Genes, Reporter; D005814:Genes, Viral; D006515:Hepatitis B virus / Q000201:enzymology* / Q000235:genetics* / Q000502:physiology; D006801:Humans; D007763:Lac Operon; D009154:Mutation; D010443:Peptide Chain Termination, Translational; D010957:Plasmids / Q000235:genetics; D014176:Protein Biosynthesis; D012194:RNA-Directed DNA Polymerase / Q000235:genetics*; D012270:Ribosomes / Q000378:metabolism; D014779:Virus Replication / Q000235:genetics
chemical_list: D015684:Gene Products, pol; C066027:P protein, Hepatitis B virus; D012194:RNA-Directed DNA Polymerase