Phosphorylation of eukaryotic translation initiation factor 2␣ (eIF2␣) is a common cellular mechanism to limit protein synthesis in stress conditions. Baculovirus PK2, which resembles the C-terminal half of a protein kinase domain, was found to inhibit both human and yeast eIF2␣ kinases. Insect cells infected with wild-type, but not pk2-deleted, baculovirus exhibited reduced eIF2␣ phosphorylation and increased translational activity. The negative regulatory effect of human protein kinase RNA-regulated (PKR), an eIF2␣ kinase, on virus production was counteracted by PK2, indicating that baculoviruses have evolved a unique strategy for disrupting a host stress response. PK2 was found in complex with PKR and blocked kinase autophosphorylation in vivo, suggesting a mechanism of kinase inhibition mediated by interaction between truncated and intact kinase domains.
The in vivo fate of amphotropic murine leukemia retrovirus was studied in five rhesus monkeys. Retrovirus infused intravenously into 3 normal animals and 1 immunosuppressed animal was cleared rapidly from the circulation and subsequent viremia has not been detected (mean follow-up of 27.4 months). A fifth monkey was immunosuppressed and transplanted with virus-producing autologous fibroblasts in addition to an intraperitoneal injection of virus. This animal was viremic for 2 days and its lymph node cells and peripheral blood mononuclear cells were shown to be producing virus for up to 22 days post-inoculation, but subsequently has been negative after 17.0 months of analysis. In the 5 animals studied (combined mean follow-up of 25.7 months), clinical illness has not been identified at any time. Therefore, murine amphotropic retroviruses do not appear to pose an acute health risk.
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