To further understand the mechanism of the NSs-mediated PKR downregulation, we examined whether NSs expression promoted degradation of PKR mRNA. 293 cells were mocktransfected or transfected with in vitro-synthesized RNA transcripts encoding NSs or rLuc. Then the cells were mock-treated or treated with ActD. Total RNAs were harvested at 8 h posttransfection and the expression levels of PKR mRNA were examined by quantitative real-time reverse transcription polymerase chain reaction (RT-PCR) analysis ( Figure 7C ). The relative expression levels of PKR mRNA were significantly increased in cells that were transfected with rLuc RNA transcripts or NSs RNA transcripts both in the absence and presence of ActD, which demonstrated to us that NSs expression did not promote the degradation of PKR mRNA. Efficient ActD-mediated suppression of IFN-b mRNA accumulation in rMP-12-rLuc-infected 293 cells ( Figure 6C ) led us to suggest that unexpected increases in the abundance of PKR mRNA in the RNA-transfected 293 cells in the presence of ActD were IFN-b-independent. We suspect that the RNA transcripts that were taken up by the cells induced robust PKR mRNA synthesis prior to ActD-or NSs-mediated general transcription suppression.