an adaptor protein that may regulate the function of receptor and cytoskeleton-associated tyrosine kinases. A class E vacuolar protein sorting (VPS) factor involved in concentration and sorting of cargo proteins of the multivesicular body (MVB) for incorporation into intralumenal vesicles. Fusion between endosomes and the vacuole will then target the cargo proteins to the vacuolar lumen. In case of infection, the HIV-1 virus directly takes advantage of its function for viral exocytosis and budding, via its interaction with HIV-1 p6 protein. May play a role in the regulation of both apoptosis and cell proliferation. Note: This description may include information from UniProtKB.