To further confirm these data, viral protein accumulation and replication were analyzed in wt mouse embryonic fibroblast (MEF) cells and in Pkr 0/0 MEF cells lacking a functional PKR expression [37] . MP-12 efficiently replicated in both wt MEF and Pkr 0/0 MEF cells, and ActD treatment had little effect on N protein accumulation and virus replication ( Figure 5E , top and middle panels). rMP12-rLuc replication was not as efficient as MP-12 in wt MEF cells in the absence of ActD for an as yet unidentified reason ( Figure 5E , middle panel). In ActD-treated wt MEF cells, both rMP-12-C13type and rMP12-rLuc failed to efficiently accumulate N proteins, and rMP-12-rLuc replicated poorly, whereas rMP-12-rLuc underwent efficient N protein accumulation and viral replication in ActD-treated Pkr 0/0 MEF cells ( Figure 5E , top and middle panels). Furthermore, accumulation of phosphorylated eIF2a did not occur in Pkr 0/0 MEF cells that were infected with rMP12-rLuc in the presence of transcriptional inhibitors 