Protein architecture of avian reovirus S1133 and identification of the cell attachment protein.

There are a number of discrepancies in the literature regarding the protein composition of the avian reoviruses. The present study demonstrates that avian reovirus S1133 contains at least 10 proteins (lambdaA, lambdaB, lambdaC, muA, muB, muBC, muBN, sigmaA, sigmaB, and sigmaC). Polypeptides muB, muBC, muBN, sigmaB, and sigmaC are components of the outer capsid layer of the virus, while lambdaA, lambdaB, muA, and sigmaA are core polypeptides. Protein lambdaC is a component of both layers, extending from the inner core to the outer capsid. The minor outer-capsid polypeptide sigmaC is shown to be the cell attachment protein, since it is the only viral polypeptide present in extracts of S1133-infected cells that binds specifically to chicken embryo fibroblasts; furthermore, its binding to avian cells was competitively inhibited by S1133 reovirions but not by mammalian reovirions. Our results also show that sigmaC is an oligomeric protein both in the virion and free in the cytoplasm, and preliminary results suggest that the multimer is made up of three monomeric units.