EIF2AK3 and cytomegalovirus infection: Interestingly, neither the precursor nor the mature form of SREBP2 were affected by PERK depletion in mock- and HCMV-infected cells (Fig. 5D), indicating that SREBP1 and SREBP2 are cleaved by different mechanisms in HCMV infection, and PERK is necessary for the cleavage of SREBP1 only.