Usurpation of the Ras signaling pathway by reovirus. In untransformed, reovirus-resistant cells, double-stranded RNA structures in reovirus transcripts activate PKR, which subsequently phosphorylates eIF-2α, inhibiting translation initiation of viral genes. In cells with an activated Ras signaling pathway, however, PKR phosphorylation in response to viral transcripts is inhibited and viral translation proceeds unimpeded.