CYTOPATHOGENICITY OF BORDER DISEASE VIRUS IS CORRELATED WITH INTEGRATION OF CELLULAR SEQUENCES INTO THE VIRAL GENOME

Two border disease virus (BDV) pairs each consisting of cytopathogenic (cp) and non-cp viruses have been analyzed at the molecular level. Wi thin the NS2-3 (p125) encoding region of both cp viruses, insertions o f cellular sequences were identified which were absent in the correspo nding non-cp isolates. A comparative sequence analysis revealed that w ithin each pair the cp and non-cp viruses are almost identical. This s trongly suggests that the cp BDV isolates developed from the non-cp vi ruses by RNA recombination between the viral genome and cellular seque nces. Nonstructural protein NS3 (p80) was demonstrated after infection with both cp BDV strains. In addition, fusion proteins composed of ce llular and viral sequences were identified. In contrast, expression of NS3 and the fusion proteins was not found after infection with the re spective non-cp counterparts.