ATF4 and infection: While PERK-/- cells showed robust eIF2α-P early in infection along with a rise in ATF4 mRNA levels starting at 2 hpi (Fig 2A and 2B, S3B Fig), eIF2α-P was detected in the combined GCN2-/-PERK-/- cells only after 24 hpi, followed by an increase in ATF4 mRNA levels at 36 hpi (Fig 2C and 2D, S3C Fig).