title: Hepatitis B viral polymerase fusion proteins are biologically active and can interact with the hepatitis C virus core protein in vivo.
abstract: Hepadnaviruses and retroviruses are evolutionarily related families because they both require a process of reverse transcription for genome replication. However, hepadnaviruses produce polymerase (pol) and core proteins separately, while retroviruses synthesize a gag-pol fusion protein that is subsequently cleaved by a virally encoded protease to release a functional polymerase. To test whether an additional sequence at the N-terminus of pol in hepatitis B virus (HBV) interferes with its function, we created two plasmids expressing core-pol fusion proteins, core144-pol and core31-pol. Secreted particles obtained from HuH-7 cells, which were cotransfected with a core-pol fusion protein-expressing plasmid and a core-expressing plasmid, showed a positive signal of HBV DNA by the endogenous polymerase assay, indicating that the core-pol fusion proteins retain DNA priming, polymerization and RNase H activities. The fusion protein was detected in the cytoplasm of transfected cells and in secreted virions by immunoprecipitation. Furthermore, we found by immunofluorescence staining that the HBV core-pol fusion protein colocalized with the hepatitis C virus (HCV) core protein in cytoplasm and in lipid droplets. Immunoprecipitation studies showed that the anti-HCV core complex contained the HBV core-pol fusion protein while the anti-HBV pol complex contained the HCV core protein, which supports the hypothesis that the HCV core protein can form a complex with the HBV core-pol fusion protein.
authors.affiliation: Institute of Microbiology and Immunology, National Yang-Ming University, Taipei, Taiwan, ROC.
authors.forename: K L
authors.initials: KL
authors.lastname: Chen
authors.forename: C M
authors.initials: CM
authors.lastname: Chen
authors.forename: C M
authors.initials: CM
authors.lastname: Shih
authors.forename: H L
authors.initials: HL
authors.lastname: Huang
authors.forename: Y H
authors.initials: YH
authors.lastname: Lee
authors.forename: C
authors.initials: C
authors.lastname: Chang
authors.forename: S J
authors.initials: SJ
authors.lastname: Lo
mesh_terms: D003593:Cytoplasm / Q000737:chemistry; D019143:Evolution, Molecular; D015684:Gene Products, pol / Q000235:genetics / Q000378:metabolism* / Q000502:physiology; D006512:Hepatitis B Core Antigens / Q000235:genetics / Q000378:metabolism* / Q000502:physiology; D006801:Humans; D008856:Microscopy, Fluorescence; D011233:Precipitin Tests; D011485:Protein Binding; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism* / Q000502:physiology; D012190:Retroviridae; D014162:Transfection; D014407:Tumor Cells, Cultured; D014758:Viral Core Proteins / Q000378:metabolism*; D014771:Virion / Q000737:chemistry
chemical_list: D015684:Gene Products, pol; D006512:Hepatitis B Core Antigens; C066027:P protein, Hepatitis B virus; D011993:Recombinant Fusion Proteins; D014758:Viral Core Proteins; C069130:nucleocapsid protein, Hepatitis C virus