TSG101/mammalian VPS23 and mammalian VPS28 interact directly and are recruited to VPS4-induced endosomes

Class E vacuolar protein sorting (vps) proteins are required for appropriat e sorting of receptors within the yeast endocytic pathway, and most probabl y function in the biogenesis of multivesicular bodies. We have identified t he mammalian orthologue of Vps28p as a 221-amino acid cytosolic protein tha t interacts with TSG101/ mammalian VPS23 to form part of a multiprotein com plex. Co-immunoprecipitation and cross-linking experiments demonstrated tha t hVPS28 and TSG101 interact directly and that binding requires structural information within the conserved C-terminal portion of TSG101. TSG101 and h VPS28 are predominantly cytosolic. However, when endosomal vacuolization wa s induced by the expression of a dominant-negative mutant of another class E vps protein, human VPS4, a portion of both TSG101 and hVPS28 translocated to the surface of these vacuoles. We conclude that TSG101 and its interact ing components are directly involved in endosomal sorting.