A short leucine-rich sequence in the Borna disease virus p10 protein mediates association with the viral phospho- and nucleoproteins

Borna disease virus (BDV) is unique among the non-segmented negative-strand RNA viruses of animals and man because it transcribes and replicates its g enome in the nucleus of the infected cell. It has recently been discovered that BDV expresses a gene product of 87 amino acids, the p10 protein, from an open reading frame that overlaps with the gene encoding the viral p24 ph osphoprotein. In addition, the p10 protein has been localized to intranucle ar BDV-specific clusters containing viral antigens, Here, characterization of p10 interactions with the viral nucleoprotein p38/p39 and the p24 phosph oprotein is reported. Immunoaffinity chromatography demonstrated the presen ce of high-salt stable complexes of p10 containing the p24 and p38/p39 prot eins in extracts of BDV-infected cells. Analyses in the yeast two-hybrid sy stem and biochemical co-precipitation experiments suggested that the p10 pr otein binds directly to the p24 phosphoprotein and indirectly to the viral nucleoprotein. Mutational analysis demonstrated that a leucine-rich stretch of amino acids at positions 8-15 within the p10 protein is critical for in teraction with p24. Furthermore, binding of p10 to the viral phosphoprotein was shown to be important for association with the BDV-specific intranucle ar clusters that may represent the sites of virus replication and transcrip tion in infected cells. These findings are discussed with respect to possib le roles for the p10 protein in viral RNA synthesis or ribonucleoprotein tr ansport.