A Functional Study of Phosphorylation of Small Hepatitis Delta Antigen on Viral Antigenomic RNA Replication
| Autor: | Shiao-Ya Hong, 洪小雅 |
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| Rok vydání: | 2010 |
| Druh dokumentu: | 學位論文 ; thesis |
| Popis: | 98 Hepatitis delta virus (HDV) is the simplest RNA virus that employs a unique strategy for viral replication. Once the virus enters the cells, it uses cellular RNA polymerases and one viral protein, small hepatitis delta antigen (SHDAg), for viral RNA replication. Recent studies have revealed that posttranslational modifications (e.g., phosphorylation, acetylation, and methylation) of SHDAg are conducting the essential functions at successive stages of the HDV life cycle. Phosphorylation of SHDAg at Ser177 is required for HDV replication from antigenomic to genomic RNA, and this residue is crucial for interaction with RNA polymerase II (RNAP II), the enzyme assumed to be responsible for antigenomic RNA replication. This study demonstrated that SHDAg dephosphorylated at Ser177 interacted preferentially with hypophosphorylated RNAP II (RNAP IIA), which generally binds at the transcription initiation sites. In contrast, the Ser177-phosphorylated counterpart (pSer177-SHDAg) exhibited preferential binding to hyperphosphorylated RNAP II (RNAP IIO). In addition, RNAP IIO associated with pSer177-SHDAg was hyperphosphorylated at both the Ser2 and Ser5 residues of its carboxyl-terminal domain (CTD), which is a hallmark of the transcription elongation isoform. Moreover, the RNAP II CTD kinase inhibitor 5,6-dichloro-1-β-D-ribofuranosyl- benzimidazole (DRB) not only blocked the interaction between pSer177-SHDAg and RNAP IIO, but also inhibited HDV antigenomic replication. Our results suggest that the phosphorylation of SHDAg at Ser177 shifted its affinity toward the RNAP IIO isoform and thus may be a switch for HDV antigenome replication, from the initiation to the elongation stage. Except for RNAP II, the study of whether SHDAg interacts with some unknown factors essential for viral replication through a phosphorylation-dependent manner is ongoing. |
| Databáze: | Networked Digital Library of Theses & Dissertations |
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