EIF2AK3 (Eukaryotic translation initiation factor 2-alpha kinase 3; PERK) is a Ser/Thr protein kinase. It phosphorylates the alpha subunit of eukaryotic translation-initiation factor 2 (EIF2), leading to its inactivation and to a rapid reduction of translational initiation and repression of global protein synthesis. PERK serves as a critical effector of unfolded protein response (UPR)-induced G1 growth arrest due to the loss of cyclin D1. Defects in PERK are the cause of Wolcott-Rallison syndrome, an early-onset diabetes mellitus.