The DDI1 (DNA Damage Inducible 1) protein, also known as VPS11B or retroviral-like aspartic protease, is a conserved eukaryotic protein implicated in cellular stress responses and protein quality control. It belongs to the retroviral aspartic protease family and contains a ubiquitin-associated (UBA) domain and a conserved aspartic protease domain. DDI1 plays a role in the ubiquitin-proteasome system (UPS), facilitating the clearance of misfolded proteins and damaged organelles. It interacts with proteasomal components and is involved in DNA damage repair pathways, particularly under genotoxic stress. DDI1 antibodies are essential tools for studying these processes, enabling detection of endogenous DDI1 expression via Western blotting, immunofluorescence, or immunoprecipitation. Research using these antibodies has highlighted DDI1's dual functionality: its protease activity may process specific substrates, while its UBA domain mediates interactions with ubiquitinated proteins. Dysregulation of DDI1 has been linked to neurodegenerative diseases and cancer, where impaired protein degradation contributes to pathogenesis. Recent studies also suggest a role in HIV-1 viral integration, as DDI1's retroviral-like domain shares structural similarities with viral proteases. However, its precise physiological substrates and regulatory mechanisms remain under investigation. DDI1 antibodies thus serve as critical reagents for unraveling its contributions to cellular homeostasis, stress adaptation, and disease pathways.