Expression of LMP1 results in phosphorylation of eIF2α in PKR^−/− and wt PERK but not in PERK^−/− mouse embryo fibroblasts (MEF). PERK^−/− MEFs were transfected with wild-type mouse PERK-myc; a clone that stably expressed PERK-myc was selected and termed wt PERK. PERK^−/−, PKR^−/−, and wt PERK MEFs were infected with a control retrovirus or a retrovirus that expresses LMP1 for 48 hours, and they were untreated or treated with 2.5 μg/mL tunicamycin for 4 hours. The cells were harvested and analyzed by Western blotting using anti–phosphorylated eIF2α, anti–total eIF2α, and anti-LMP1 antibodies. The ratios of phosphorylated eIF2α to total eIF2α were calculated. The numbers represent the fold difference of induced ratios relative to the uninduced ratios. *P (2-sided) <.05, Wilcoxon signed rank test. A representative example of 4 independent experiments is shown.