Antigenic relationship and further characterization of two major Borna disease virus-specific proteins.

After immunization of mice with isolated Borna disease virus (BDV)-specific proteins having Mrs of 38/39K and 24K, monoclonal antibodies (MAbs) were obtained which were specific for one of the antigens in Western blot analysis. However, in immunoprecipitation assays it was found that some MAbs of each specificity reacted exclusively with their respective antigen from BDV-infected cells, whereas other MAbs coprecipitated the heterologous protein. The relationship between the 38/39K and 24K proteins was demonstrated by two-dimensional peptide mapping, which revealed four identical peptides. Additionally, it was found that neither the 38/39K nor the 24K protein is glycosylated, but that the 24K protein is phosphorylated at serine residues. Experiments employing various cell separation protocols revealed that the 38/39K and the 24K proteins are evenly distributed within infected cells; this was confirmed by immunofluorescence techniques using 38/39K- or 24K-specific MAbs. Iodination experiments clearly demonstrated that only the 38/39K protein is expressed on the surface of virus-infected cells.

The 24K protein of Borna disease virus.

Based on partial amino acid sequences obtained from tryptic peptides of the purified 24K antigen of Borna disease virus (BDV), we identified and sequenced four independent cDNA clones established from BDV-infected MDCK cells. Each of the clones encodes a polypeptide of 201 residues (Mr 22461) that differs considerably from an amino acid sequence published recently. In vitro transcription/translation of both the wild-type and a 5' truncated clone lacking the first ATG codon yielded a peptide that comigrates on electrophoresis with a polypeptide immunoprecipitated from BDV-infected cells. The deduced amino acid sequence contains a putative signal for nuclear targeting.