The negative regulator of Borna disease virus polymerase is a non-structural protein.
The X protein of Borna disease virus (BDV) negatively regulates viral polymerase activity. With a BDV mini-replicon system, 30 % inhibition of polymerase activity was observed at an X to phosphoprotein (P) plasmid ratio of 1:6 and 100 % inhibition at a ratio of 1:1. It was therefore hypothesized that (i) the X:P ratio in infected cells is not significantly higher than 1:6 to prevent complete inhibition of polymerase activity and (ii) X is not efficiently incorporated into viral particles, allowing efficient replication early in infection. To test these assumptions, a monoclonal antibody directed against BDV X was generated. Immunofluorescence analysis revealed co-localization of X with the nucleoprotein (N) and P in the nucleus, as well as in the cytoplasm of BDV-infected cells. Quantification of viral protein levels by Western blot analysis, using purified Escherichia coli-derived X, P and N as protein standards, revealed an X:P:N ratio in BDV-infected cells of approximately 1:6:40. However, only traces of X could be detected in purified BDV stock, suggesting that X is excluded from virus particles. These results indicate that X is a non-structural protein. The lack of X in virus particles may facilitate polymerase activity early in infection; however, the presence of X in persistently infected cells may result in partial inhibition of the polymerase and thus contribute to viral persistence.
Schwardt
Malte
M
Department of Virology, University of Freiburg, Hermann-Herder-Strasse 11, D-79104 Freiburg, Germany.
Mayer
Daniel
D
Department of Virology, University of Freiburg, Hermann-Herder-Strasse 11, D-79104 Freiburg, Germany.
Frank
Ronald
R
Department of Chemical Biology, GBF, Braunschweig, Germany.
Schneider
Urs
U
Department of Virology, University of Freiburg, Hermann-Herder-Strasse 11, D-79104 Freiburg, Germany.
Eickmann
Markus
M
Institut für Virologie, Universität Marburg, Germany.
Planz
Oliver
O
Institut für Immunologie, Friedrich Loeffler-Institut, Tübingen, Germany.
Wolff
Thorsten
T
Robert Koch-Institut, D-13353 Berlin, Germany.
Schwemmle
Martin
M
Department of Virology, University of Freiburg, Hermann-Herder-Strasse 11, D-79104 Freiburg, Germany.
D000818:Animals; D001891:Borna disease virus / Q000201:enzymology* / Q000235:genetics / Q000378:metabolism; D012321:DNA-Directed RNA Polymerases / Q000037:antagonists & inhibitors* / Q000378:metabolism; D004791:Enzyme Inhibitors / Q000378:metabolism; D015967:Gene Expression Regulation, Viral / Q000502:physiology*; D005809:Genes, Regulator; D016679:Genome, Viral; D009698:Nucleoproteins / Q000235:genetics / Q000378:metabolism; D017361:Viral Nonstructural Proteins / Q000378:metabolism / Q000502:physiology*
D004791:Enzyme Inhibitors; D009698:Nucleoproteins; D017361:Viral Nonstructural Proteins; D012321:DNA-Directed RNA Polymerases