| Summary: | 博士 === 國立臺灣大學 === 生化學研究所 === 86 === Hepatitis delta virus (HDV) is a satellite virus of hepatitis B virus and is a human pathogen causing fulminant hepatitis and liver cirrhosis. HDV contains a single-stranded circular KNA genome of 1.7 kb in length. The genomic KNA possesses extensive intramolecular complementary sequences that form an unbranched rod-like structure. Hepatitis delta antigen (HDAg) is a nuclear phosphoprotein and present in HDV as two forms, small HDAg (HDAg-S, 24 kDa, 195 amino acids) and large HDAg (HDAg-L, 27 kDa, 214 amino acids). The two proteins are identical in sequence, except that the HDAg-L contains an additional 19 amino acids at its C terminus as a result of a specific point mutation. There is an isoprenylation motif (CRPQ-214) at the extreme C-terniinus of HDAg-L which undergoes famesylation. The HDAgs possess RNA-binding activity and form RNP complexes with HDV RNA within HDV particles. Functions of the two forms of HDAg are quite different. The HDAg-S is required for HDV RNA replication, whereas the HDAg-L has negative effects on genome replication and is required for HDV assembly. The unique C-terminal domain of HDAg-L may have implications for the specific functions of HDAg-L involved in HDV assembly. The aims of this study are to elucidate the mechanisms by which HDAgs and cellular factors are involved in HDV assembly and replication.
Saturated substitution mutants from amino acids 198 to 210 that are franking the isoprenylation motif of the HDAg-L were generated, Two single-substitution mutants at 198Leu->Arg and 205Pro->Ala respectively were found to be completely loss virion assembly ability. These results suggest that both Leu-199 and Pro-205 are critical for virion assembly. Indirect immunofluorescent staining was performed with cultured cells transfected with a large HDAg-encoding plasmid. The HDAg-L appeared to be cytoplasm-localized in the presence of HBsAg.
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