Progress and controversy in Bornavirus research: a meeting report
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Virology Division News Arch Virol 144/4 (1999)
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Virology Division News
Progress and controversy in Bornavirus research: a meeting report M. Schwemmle Institut für Medizinische Mikrobiologie und Hygiene, Freiburg, Federal Republic of Germany
Introduction Borna disease virus (BDV) is the type species of a new family, Bornaviridae, within the nonsegmented negative-strand RNA viruses (Mononegavirales). Unlike other members of the order Mononegavirales BDV replicates and transcribes in the nucleus and uses the splicing machinery for modification of subgenomic RNAs. The host range includes a broad variety of warmblooded animals and most likely humans. BDV is neurotropic and infection of immunocompetent animals can result in Borna disease (BD), an immune-mediated brain disorder, characterised by prominent disturbances of movement and behaviour. First hints that BDV could also be associated with certain human diseases emerged from serological studies beginning in the 80’s when psychiatric patients were found to be seropositive in an indirect immunfluorescence assay (IFA). Ever since then, the question of whether BDV infections cause psychiatric disorders in humans has remained a controversial issue. An international meeting was held in Freiburg* to discuss progress and controversial topics in Bornavirus research. Among the highlights were aspects of the molecular biology of BDV, the neuropathology of BDV-infected animals and first reports on the multicenter studies in Germany and Japan that evaluated the methods for detection of BDV in humans. Molecular biology of BDV BDV encodes at least six proteins including the nucleoprotein (N), the phosphoprotein (P), a putative matrixprotein (gp18), the glycoprotein (G), the polymerase (pol) and the just recently identified X-protein. Very little is known about the function of these proteins. Colocalization studies indicated that P, N and X are part of the ribonucleoprotein particles. Binding studies with individual proteins indicated that P might bind X and N at nonoverlapping binding sites. Using various experimental approaches two groups from Giessen/ Marburg and Freiburg/Irvine [16, 18] presented data that the X-protein is a nuclear export protein containing leucine-rich nuclear export sequences (NESs). Yeast two hybrid experiments revealed a specific binding of X to the cellular NES-binding protein CRM1 (Exportin). Intriguingly, mutation of the critical leucine residues within the NES did not only * Bornavirus Meeting, 27–29 September 1998, Freiburg, Germany.
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abrogate binding to CRM1 but also to P, indicating that the binding site for P is overlapping with the NES of X. It was speculated that this masking of the NES of X by P could be critical for the efficient import of X into the nucleus. Whether X is involved in nuclear export of viral RNPs, like NS2 of influenza virus, or in nuclear export of viral transcripts, is currently being investigated. New insights into the biology of the glycoprotein G were presented by O. Lenz (Marburg) [11].
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