 Normally, the 5′untranslated region (5′UTR) in the BACE1 promoter would fundamentally inhibit the expression of BACE1 gene.However, BACE1 expression can be activated by phosphorylation of eIF2a, which reverses the inhibitory effect exerted by BACE1 5′UTR.Phosphorylation of eIF2a is triggered by activation of PKR.