Component of the ESCRT-I complex, a regulator of vesicular trafficking process. Binds to ubiquitinated cargo proteins and is required for the sorting of endocytic ubiquitinated cargos into multivesicular bodies (MVBs). Mediates the association between the ESCRT-0 and ESCRT-I complex. Required for completion of cytokinesis; the function requires CEP55. May be involved in cell growth and differentiation. Acts as a negative growth regulator. Required for the exosomal release of SDCBP, CD63 and syndecan (By similarity). It may also play a role in the extracellular release of microvesicles that differ from the exosomes (By similarity). Component of the ESCRT-I complex (endosomal sorting complex required for transport I) which consists of TSG101, VPS28, a VPS37 protein (VPS37A to -D) and MVB12A or MVB12B in a 1:1:1:1 stoichiometry. Interacts with VPS37A, VPS37B and VPS37C. Interacts with DMAP1. Interacts with ubiquitin (By similarity). Interacts with AATF (PubMed:14761944). Interacts with stathmin and GMCL (By similarity). 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 HGS; the interaction mediates the association with the ESCRT-0 complex. Interacts with GGA1 and GGA3. Interacts (via UEV domain) with PDCD6IP/AIP1. Interacts with VPS28, SNF8 and VPS36. Self-associates. Interacts with MVB12A; the association appears to be mediated by the TSG101-VPS37 binary subcomplex. Interacts with VPS37D. Interacts with LRSAM1. Interacts with CEP55; the interaction is required for cytokinesis. Interacts with PDCD6. Interacts with LITAF. Interacts with MGRN1 (By similarity). Interacts with ARRDC1; recruits TSG101 to the plasma membrane (By similarity). Mainly cytoplasmic. Membrane-associated when active and soluble when inactive. Nuclear localization is cell cycle-dependent. Interaction with CEP55 is required for localization to the midbody during cytokinesis. The UEV domain is required for the interaction of the complex with ubiquitin. The coiled coil domain may interact with stathmin. Monoubiquitinated at multiple sites by LRSAM1 and by MGRN1. Ubiquitination inactivates it, possibly by regulating its shuttling between an active membrane-bound protein and an inactive soluble form. Ubiquitination by MGRN1 requires the presence of UBE2D1. Belongs to the ubiquitin-conjugating enzyme family. UEV subfamily.