AUP1 is involved in several pathways, including quality control of misfolded proteins in the endoplasmic reticulum and lipid droplet accumulation. Lipid droplets are cytoplasmic organelles that store neutral lipids such as cholesterol esters and triglycerides. This storage prevents an overabundance of free cholesterol and fatty acids in cells, and also supplies lipids for other metabolic processes, such as membrane biogenesis. Reduced expression of the AUP1 gene results in reduced lipid droplet clustering, a function that depends on ubiquitination of the protein.

The AUP1 protein contains several domains: a hydrophobic N-terminal domain, an acetyltransferase domain, a ubiquitin-binding CUE domain and a UBE2B2-binding domain (G2BR). UniProt places it in the AUP1 family, and HGNC classifies it within the CUE domain containing gene group. Its subcellular locations include the endoplasmic reticulum membrane, lipid droplets and autophagosomes. Alternative splicing of the gene results in multiple transcript variants.

In the context of microbial infection, UniProt records that following Dengue virus infection AUP1 is required for the induction of lipophagy, which facilitates production of virus progeny particles. The protein name reflects its role in VLDL assembly regulation, while the earlier name, ancient ubiquitous protein 1, is still found in the literature. Orthologues are named Aup1 in both mouse and rat.