Generation of bovine respiratory syncytial virus (BRSV) from cDNA: BRSV NS2 is not essential for virus replication in tissue culture, and the human RSV leader region acts as a functional BRSV genome promoter

In order to generate recombinant bovine respiratory syncytial virus (BRSV), the genome of BRSV strain A51908, variant ATue51908, was cloned as cDNA, W e provide here the sequence of the BRSV genome ends and of the entire L gen e, This completes the sequence of the BRSV genome, which comprises a total of 15,140 nucleotides. To establish a vaccinia virus-free recovery system, a BHK-derived cell line stably expressing T7 RNA polymerase was generated ( BSR T7/5), Recombinant BRSV was reproducibly recovered from cDNA constructs after T7 RNA polymerase-driven expression of antigenome sense RNA and of B RSV N, P, M2, and L proteins from transfected plasmids, Chimeric viruses in which the BRSV leader region was replaced by the human respiratory syncyti al virus (HRSV) leader region replicated in cell culture as efficiently as their nonchimeric counterparts, demonstrating that all cis-acting sequences of the HRSV promoter are faithfully recognized by the BRSV polymerase comp lex. In addition, we report the successful recovery of a BRSV mutant lackin g the complete NS2 gene, which encodes a nonstructural protein of unknown f unction. The NS2-deficient BRSV replicated autonomously and could be passag ed, demonstrating that NS2 is not essential for virus replication in cell c ulture. However, growth of the mutant was considerably slower than and fina l infectious titers were reduced by a factor of at least 10 compared to wil d-type BRSV, indicating that NS2 provides a supporting factor required for full replication capacity.