Aspartic protease that mediates the cleavage of NFE2L1/NRF1 at 'Leu-104', thereby promoting release of NFE2L1/NRF1 from the endoplasmic reticulum membrane (PubMed:27528193, PubMed:27676298). Ubiquitination of NFE2L1/NRF1 is a prerequisite for cleavage, suggesting that DDI2 specifically recognizes and binds ubiquitinated NFE2L1/NRF1 (PubMed:27528193). Seems to act as a proteasomal shuttle which links the proteasome and replication fork proteins like RTF2 (Probable). Required, with DDI1, for cellular survival following replication stress. Together or redundantly with DDI1, removes RTF2 from stalled forks to allow cell cycle progression after replication stress and maintains genome integrity (PubMed:29290612). {ECO:0000269|PubMed:27528193, ECO:0000269|PubMed:27676298, ECO:0000269|PubMed:29290612, ECO:0000305|PubMed:29290612}. This is the function of DDI2 (DDI proteasomal shuttling factor 2, Ensembl gene identifier ENSG00000197312).