Genetic variation during lytic reovirus infection: high-passage stocks of wild-type reovirus contain temperature-sensitive mutants.

Wild-type clones of reovirus serotypes 1 (Lang), 2 (Jones), and 3 (Dearing) were serially passaged in L cells at a high multiplicity of infection, and the virus population was examined at passage levels 2, 5, and 11 for the presence of temperature-sensitive (ts) mutants. By passage 11 all three serotypes contained ts mutants that were not present in the original wild-type stock. ts mutants representing three mutant groups were identified. The majority of these mutants were in group G. Our results show that high-passage stocks of reovirus consist of a genetically heterogeneous population.     

PKR-dependent and -independent mechanisms are involved in translational shutoff during Sindbis virus infection

The replication of Sindbis virus (SIN) profoundly affects the metabolism of infected vertebrate cells. One of the main events during SIN infection is the strong inhibition of translation of cellular mRNAs. In this study, we used a combination of approaches, including the study of SIN replication in PKR(-/-) mouse embryo fibroblasts or in the presence of an excess of catalytically inactive PKR. We show that the PKR-dependent inhibition of translation is not the only and most likely not the major pathway mediating translational shutoff during SIN infection. The PKR-independent mechanism strongly affects the translation of cellular templates, whereas translation of SIN subgenomic RNA is resistant to inhibition, and this leads to a benefit for viral replication. Our findings suggest that both PKR-dependent and non-PKR-dependent mechanisms of SIN-induced translational shutoff can be manipulated by using SIN replicons expressing mutated SIN nsP2 or kinase-defective PKR. Specifically, we show that expression of heterologous genes from SIN-based and most likely other alphavirus-based replicons can be increased by downregulating both the PKR-dependent and PKR-independent translational shutoffs.