The function of reovirus proteins during the reovirus multiplication cycle: analysis using monoreassortants.

When cultured cells are injected with mixtures of cores of two reovirus strains, a high proportion of reassortants are monoreassortants, that is, virus particles that contain one genome segment of 1 parent and 9 genome segments of the other. We have isolated two complete sets of monoreassortants, those that contain a single serotype 2 genome segment and 9 serotype 3 genome segments, and those that contain 1 serotype 3 genome segment and 9 serotype 1 genome segments. We have used the former set of monoreassortants (because reovirus serotypes 2 and 3 are less closely related than serotypes 1 and 3) to assess the effect of all 10 genome segments, or rather of the proteins that they encode, in controlling parameters of the reovirus multiplication cycle such as yield size, extent of viral ssRNA, dsRNA and protein synthesis, plaque size, and cytopathogenicity. Among the major findings are: proteins lambda 2, mu 1/mu 1C, and sigma 3 control yield size and extent of RNA and protein synthesis; proteins mu 2 and sigma 1 control severity of cytopathic effects; and proteins sigma 1, mu 1/mu 1C, and mu 2 control plaque size. Identification of monoreassortant phenotypes is useful for identifying which viral proteins are functionally involved at the various stages of the reovirus multiplication cycle.