Protein kinase-like endoplasmic reticulum kinase (PERK) is an eIF2? kinase and transmembrane protein resident in the endoplasmic reticulum (ER) membrane that couples ER stress signals to translation inhibition . ER stress increases the activity of PERK, which then phosphorylates eIF2? to promote reduced translation. Research studies have demonstrated that PERK-deficient mice have defects in pancreatic ? cells several weeks after birth, suggesting a role for PERK-mediated translational control in protecting secretory cells from ER stress . PERK activation during ER stress correlates with autophosphorylation of its cytoplasmic kinase domain . Phosphorylation of PERK at Thr980 serves as a marker for its activation status.