SEQUENCE AND GENOME ORGANIZATION OF BORNA-DISEASE VIRUS

We have previously demonstrated that Borna disease virus (BDV) has a n egative nonsegmented single-stranded (NNS) RNA genome that replicates in the nucleus of infected cells. Here we report for the first time th e cloning and complete sequence of the BDV genome. Our results reveale d that BDV has a genomic organization similar to that of other members of the Mononegavirales order. We have identified five main open readi ng frames (ORFs). The largest ORF, V, is located closest to the 5' end in the BDV genome and, on the basis of strong homology with other NNS -RNA virus polymerases, is a member of the L-protein family. The inter cistronic regions vary in length and nucleotide composition and contai n putative transcriptional start and stop signals. BDV untranslated 3' and 5' RNA sequences resemble those of other NNS-RNA viruses. Using a set of overlapping probes across the BDV genome, we identified nine i n vivo synthesized species of polyadenylated subgenomic RNAs complemen tary to the negative-strand RNA genome, including monocistronic transc ripts corresponding to ORFs I, II, and IV, as well as six polycistroni c polyadenylated BDV RNAs. Interestingly, although ORFs III and V were detected within polycistronic transcripts, their corresponding monoci stronic transcripts were not detected. Our data indicate that BDV is a member of the Mononegavirales, specially related to the family Rhabdo viridae. However, in contrast to the rest of the NNS-RNA animal viruse s, BDV replication and transcription occur in the nucleus of infected cells. These findings suggest a possible relationship between BDV and the plant rhabdoviruses, which also replicate and transcribe in the nu cleus.