D型肝炎病毒之小型 Delta 抗原與 DNA- 依賴性 RNA 聚合酶 I 之交互作用

Abstract

Hepatitis delta virus (HDV) is a spherical virus particle with envelope. HDV is a satellite virus of hepatitis B virus, it contains hepatitis B surface antigens essential for viral infection. The viral particle possesses a 1.7 kb single-stranded circular RNA genome that is replicated by RNA-dependent RNA polymerase via a double rolling circle mechanism. A 0.8 kb mRNA encoding the hepatitis delta antigen (HDAg) is also generated during the viral replication. There are two forms of delta antigen, the small HDAg (HDAg-S, 24 kD) and the large HDAg (HDAg-L, 27 kD). Previsous studies indicate that host DNA-dependent RNA polymerase II (RNA pol II) is involved in the synthesis of the full length genomic RNA and mRNA of HDV. However, evidences suport that other cellular RNA polymerases are involved in the synthesis of HDV antigenomic RNA. At the early stage of viral replication, HDAg-S is localized at the nucleolus and binds to nucleolus proteins nucleolin and B23, suggesting that nucleolus-localized RNA pol I is a potential candidate for the synthesis of HDV antigenomic RNA.RNA polymerase I polypeptide A (RPA194) is the largest subunit in RNA pol I complex. It is responsible for ribosomal RNA transcription elongation. In this study, interaction between RPA194 and HDAg-S were indicated by co-immunoprecipitation. In addition, GST pull-down assay further demonstrated that the RPA194 constant region fragment a interacted with His-tagged HDAg-S. A reporter plamid were generated to examine the effect of HDAg-S on the rDNA promoter activity. The result demonstrated that HDAg-S inhibits the synthesis of rRNA. Mechanisms involved in the RNA pol I-mediated replication of HDV antigenomic RNA remains to be elucidated.