The S1 genome segment of avian reovirus strain S1133 was cloned and completely sequenced. The sequence comprised 1636bp with three distinct open reading frames (ORFs), suggesting the gene was polycistronic in nature. The three ORFs from 5' to 3' were predicted to encode polypeptides of 9"8, 3"8 and 34.9 kDa, respectively. Of the three ORFs, only the third possessed the AUG initiation codon in an optimum context for translation. The third ORF-encoded protein, 326 amino acids in length, was expressed in Escherichia coli and used as antigen in immunoblots. The protein was concluded to be a 3 on the basis of its recognition by a chicken anti-reovirus antiserum and due to the fact that a mouse antiserum raised against it recognized specifically the viral a3 polypeptide. Sequence comparison of the avian reovirus S 1 gene with its mammalian counterpart did not show any significant similarity between the two. However, amino acid sequence analysis and the predicted existence of a heptapeptide repeat pattern, as well as the relatively high frequency of or-helix structures in the amino terminal portion of a3 suggests that this protein is structurally, and probably functionally, related to mammalian reovirus a 1 protein.

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The prevalence of antibodies to some bovine viruses of the respiratory and digestive systems were investigated in two caribou herds in Northern Quebec, Canada, in autumn of 1978 in one herd, and 1979 in another herd. The serum neutralization and hemagglutination inhibition techniques were used. Antibody to bovine viral diarrhea was the most prevalent in the two years (69.3% in 1978 and 60.7% in 1979), followed by bovine adenovirus 3 (42.9% and 17.8%), infectious bovine rhinotracheitis virus (39.6% and 14.2%) and coronavirus (13.3% in 1978 only). Antibody to parainfluenzavirus 3 was not detected.

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It has been suggested that avian reovirus ¢r3 protein is analogous to al trimer, the mammalian reovirus attachment protein. We have investigated the multimeric nature and cell binding ability of a3 protein.The data presented here demonstrate that a3 protein is a multimer in its undisrupted form as determined by SDS-PAGE in non-dissociating conditions. However, virion-associated a3 protein and COS-7 cell-expressed protein behaved differently in SDS-PAGE, suggesting a need for virusassociated factor(s) to control the multimerization of the protein. The data also show that Escherichia coil expressed o'3 fusion protein (~r3-MBP) in its multimeric form is capable of attaching to Vero cells. The binding was found to be specific and receptor mediated by the fact that it was inhibited by a monoclonal antibody specific for a3 protein and by competition with avian reovirus particles. As determined by a reverse experiment, tr3-MBP was also able to reduce the virus p.f.u. in monolayer cell cultures, indicating the important role of a3 protein in the initiation of virus infection.