Fig. 1. eIF2α phosphorylation promotes GADD34 expression. (A) Immunoblot of GADD34, eIF2α phosphorylated on serine 51 (P-eIF2α) and total eIF2α from untreated (UT), thapsigargin (Tg)-, tunicamycin (Tm)-, or arsenite (As)-treated NIH-3T3 (Parental) cells or cells expressing a C-terminal fragment of GADD34 that constitutively dephosphorylates eIF2α (GADD34 C-term) (Novoa et al., 2001). (B) Immunoblot of GADD34, phosphorylated eIF2α and total eIF2α from untreated, thapsigargin and tunicamycin treated wild-type and PERK–/– mouse fibroblasts. (C) Immunoblot of GADD34 and total eIF2α from untreated (UT), thapsigargin (Tg; 8 h)-, tunicamycin (Tm; 8 h)- and arsenite (As; 4 h)-treated mouse embryonic fibroblasts with the indicated eIF2α genotype (upper panels). eIF2α phosphorylation was measured by immunoblot in the same cells following thapsigargin (Tg; 2 h), tunicamycin (Tm; 2 h) and arsenite (As; 2 h) treatment (lower panels).