title: The negative regulator of Borna disease virus polymerase is a non-structural protein.
abstract: 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.
authors.affiliation: Department of Virology, University of Freiburg, Hermann-Herder-Strasse 11, D-79104 Freiburg, Germany.
authors.forename: Malte
authors.initials: M
authors.lastname: Schwardt
authors.affiliation: Department of Virology, University of Freiburg, Hermann-Herder-Strasse 11, D-79104 Freiburg, Germany.
authors.forename: Daniel
authors.initials: D
authors.lastname: Mayer
authors.affiliation: Department of Chemical Biology, GBF, Braunschweig, Germany.
authors.forename: Ronald
authors.initials: R
authors.lastname: Frank
authors.affiliation: Department of Virology, University of Freiburg, Hermann-Herder-Strasse 11, D-79104 Freiburg, Germany.
authors.forename: Urs
authors.initials: U
authors.lastname: Schneider
authors.affiliation: Institut für Virologie, Universität Marburg, Germany.
authors.forename: Markus
authors.initials: M
authors.lastname: Eickmann
authors.affiliation: Institut für Immunologie, Friedrich Loeffler-Institut, Tübingen, Germany.
authors.forename: Oliver
authors.initials: O
authors.lastname: Planz
authors.affiliation: Robert Koch-Institut, D-13353 Berlin, Germany.
authors.forename: Thorsten
authors.initials: T
authors.lastname: Wolff
authors.affiliation: Department of Virology, University of Freiburg, Hermann-Herder-Strasse 11, D-79104 Freiburg, Germany.
authors.forename: Martin
authors.initials: M
authors.lastname: Schwemmle
mesh_terms: 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*
chemical_list: D004791:Enzyme Inhibitors; D009698:Nucleoproteins; D017361:Viral Nonstructural Proteins; D012321:DNA-Directed RNA Polymerases