PERK is a transmembrane protein that resides in the ER. PERK, when activated, initiates the unfolded protein
response (UPR) in the cells. You found a mutant cell line that is unable to carry out the UPR. Upon close examination using immunostaining you found that in the mutant cells, most of the PERK accumulates in the Golgi. You concluded that this is caused by a mutation in the PERK protein itself. What is the likely mutation that would result in such phenotype?