Component of the ESCRT-I complex, a regulator of vesicular trafficking process (PubMed:31203368). Binds to ubiquitinated cargo proteins and is required for the sorting of endocytic ubiquitinated cargos into multivesicular bodies (MVBs) (By similarity). Plays a role in the proteasomal degradation of ubiquitinated cell-surface proteins, such as EGFR and BST2 (PubMed:31203368). Component of an ESCRT-I complex (endosomal sorting complex required for transport I) which consists of TSG101, VPS28, VPS37A and UBAP1 in a 1:1:1:1 stoichiometry. Interacts with PTPN23. Interacts (via UBA domains) with ubiquitinated proteins. Predominantly cytosolic. Recruited to endosomes as part of the ESCRT-I complex. Ubiquitous. Highly expressed in heart, liver, brain, kidney, spleen, skeletal muscle, stomach, testis and lung. The UMA domain mediates association with the ESCRT-I complex. Lethality by postnatal day 14 (PubMed:31203368). Conditional deletion in neurons impairs endosomal ubiquitin processing and promotes neurodegeneration (PubMed:31203368).