Probable aspartic protease (By similarity). Seems to act as a proteasomal shuttle which links the proteasome and replication fork proteins like RTF2. Required, with DDI2, for cellular survival following replication stress. Together or redudantly with DDI2, removes RTF2 from stalled forks to allow cell cycle progression after replication stress and maintains genome integrity (By similarity). Belongs to the DDI1 family.