The complete shutoff of cellular translation by puromycin for 16 h did not result in the loss of endogenous PKR ( Figure 7D ), whereas as early as 8 h post-transfection of RNA transcripts encoding NSs, the abundance of PKR decreased substantially ( Figure 7B ) without reducing the abundance of PKR mRNA ( Figure 7C ). Furthermore, NSs expression reduced the abundance of myc-tagged PKR that had been radiolabelled prior to NSs expression ( Figure 7E ). These data strongly suggested that NSs induced the downregulation of PKR at a post-transcriptional level and pointed to a possibility that the NSs promoted PKR degradation.