Avian Reovirus σC Protein Contains a Putative Fusion Sequence and Induces Fusion when Expressed in Mammalian Cells

Abstract

The biological functions of the structural protein sigma C, from avian reovirus strain RAM-1, were investigated in this study. A putative fusion peptide in sigma C was recognized in the deduced amino acid sequence by homology with Pneumovirus fusion sequences, and it was thus postulated that this protein may be involved in the formation of syncytia in cells infected with RAM-1. The sigma C gene was cloned and expressed in mammalian (COS7) cells and the sigma C protein was found to induce syncytia. It was therefore concluded that this protein is indeed responsible for avian reovirus-induced cell fusion. It was also found that sigma C caused condensation of the nuclei within a syncytium, as observed in RAM-1-infected cells. On the basis that this represented condensation of the chromatin, the inhibition of cellular DNA synthesis by the virus and by the sigma C protein was measured. It was found that the virus caused a 50% reduction in cellular DNA synthesis, but the sigma C protein did not inhibit DNA synthesis. Therefore pyknosis of the nuclei and inhibition of cellular DNA synthesis by RAM-1 are likely to be separate events.

The Avian Reovirus Genome Segment S1 Is a Functionally Tricistronic Gene That Expresses One Structural and Two Nonstructural Proteins in Infected Cells

“…Avian reovirus, together with two mammalian reoviruses, Nelson Bay virus and baboon reovirus, are fusogenic viruses that induce syncytia formation in infected cells (Duncan et al, 1995;Gard and Compans, 1970;Kamawara et al, 1965). Recent studies have revealed that the fusogenic activity of avian reovirus is associated with genome segment S1 (Duncan and Sullivan, 1998;Shmulevitz and Duncan, 2000), and two of the S1-encoded proteins, C and p10, were reported to display fusogenic activity (Meanger et al, 1999;Shmulevitz and Duncan, 2000;Theophilos et al, 1995). The third goal of this study was therefore to investigate the fusogenic properties of the proteins encoded by the three S1 ORFs.…”

Sequences of avian reovirus M1, M2 and M3 genes and predicted structure/function of the encoded μ proteins

“…The ARV S1 gene also encodes proteins p10 and p17. Although ARVs share many features with the prototypic mammalian reoviruses (MRV), several notable differences exist including host range, pathogenicity, hemagglutination properties, and syncytium formation (Ni and Ramig, 1993;Theophilos et al, 1995;Martinez-Costas et al, 1997a;Jones, 2000;van der, 2000). Genomic coding differences also exist between MRV and ARV.…”

Molecular characterization and expression of the S3 gene of muscovy duck reovirus strain 89026.

“…At least ten structural polypeptides were identified in the latter study. The minor outer-capsid polypeptide σC was shown to be the cellattachment protein and to induce serotype-specific neutralizing antibodies Wickramasinghe et al, 1993 ;Theophilos et al, 1995). This protein was suggested to be structurally analogous to mammalian σ1 Shapouri et al, 1995).…”