To determine whether NSs expression alone induces PKR downregulation, 293 cells were mock-infected or infected with rMP12-rLuc, immediately transfected with in vitro-synthesized RNA transcripts encoding rLuc or NSs, and treated with ActD ( Figure 7B, left panel) . Cells were harvested at 16 h posttransfection. The clear reduction in the PKR abundance occurred in mock-infected cells expressing NSs, but not in those expressing rLuc ( Figure 7B, left panel) , demonstrating that NSs protein alone exerted the PKR downregulation.