Ten virus-specific polypeptides ranging in molecular weight from approximately 200k to 11k were identified in bovine respiratory syncytial virus (BRSV-)infected cells. Time course analysis of the induction of the viral polypeptides indicated that they could be detected as early as 30 min post-infection and their synthesis reached a plateau 12 h after infection. Cell free translation of total infected-cell mRNA in a rabbit reticulocyte system yielded 7 proteins corresponding in size to virus-specific proteins synthesized in BRSV-infected cells. The P protein was highly phosphorylated; G and F were identified as glycoproteins by [3H]glucosamine labeling. Glycosylation of G protein was largely resistant to tunicamycin, suggesting that the majority of the carbohydrate residues are attached via O-glycosidic bonds, whereas the F protein was N-linked glycosylated. Tunicamycin caused a drastic reduction in the yield of infectious virus titer indicating that the carbohydrate moieties serve a critical role in the infectious cycle of BRSV.

Specific interactions between the nucleocapsid protein (N) and the phosphoprotein (P) of bovine respiratory syncytial virus (BRSV) have been investigated using a yeast-based two-hybrid system. Plasmids encoding the yeast GAL4 DNA binding domain fused with the N gene and GAL4 activation domain fused with the P gene were cotransfected into competent yeast cells. The ability of the N and P proteins to interact in vivo was measured by activation of the lacZ reporter gene by the GAL4 transactivation region. Results indicated that the N and P proteins interact very strongly in vivo. When interactions between N and various deletion mutants of the P protein were examined, an internal region (aa 132-168) and the highly acidic C-terminal region (aa 236-241) of the P protein were found to be essential for N-P interaction. In addition, the highly basic N-terminal region (amino acids 1--40) was found to be involved in N-P interaction to a lesser extent.

The nucleotide and deduced amino acid sequences of the phosphoprotein (P) mRNA of bovine respiratory syncytial virus (BRSV) strain A51908 have been determined. The P mRNA is 860 nucleotides long with a single large open reading frame and the encoded polypeptide is 241 amino acids long. Comparison with the corresponding sequences of human respiratory syncytial virus (HRSV) subgroups A and B revealed 72 to 74% identity at the nucleotide level, and 81% at the amino acid level. The P protein contains a single divergent domain (37 % amino acid identity) flanked by highly conserved domains (87 % amino acid identity). The 3' end non-coding region is 47 nucleotides shorter than the corresponding region of HRSV. Comparison of the P mRNA sequences of two strains of BRSV (A51908 and FS-1) showed that there was extensive sequence identity at both the nucleotide (97%) and amino acid (97-9%) levels.