Aspartic protease that mediates the cleavage of NFE2L1/NRF1 at 'Leu-104', thereby promoting release of NFE2L1/NRF1 from the endoplasmic reticulum membrane. Ubiquitination of NFE2L1/NRF1 is a prerequisite for cleavage, suggesting that DDI2 specifically recognizes and binds ubiquitinated NFE2L1/NRF1. Seems to act as a proteasomal shuttle which links the proteasome and replication fork proteins like RTF2. Required for cellular survival following replication stress. Homodimer. Belongs to the DDI1 family. Although this protein contains the conserved Asp-246 that functions as an active site, this protein does not have proteolytic activity, and may therefore be catalytically inactive.