Probable core component of the endosomal sorting required for transport complex III (ESCRT-III) which is involved in multivesicular bodies (MVBs) formation and sorting of endosomal cargo proteins into MVBs. MVBs contain intraluminal vesicles (ILVs) that are generated by invagination and scission from the limiting membrane of the endosome and mostly are delivered to lysosomes enabling degradation of membrane proteins, such as stimulated growth factor receptors, lysosomal enzymes and lipids. The MVB pathway appears to require the sequential function of ESCRT-O, -I,-II and -III complexes. ESCRT-III proteins mostly dissociate from the invaginating membrane before the ILV is released. The ESCRT machinery also functions in topologically equivalent membrane fission events, such as the terminal stages of cytokinesis. ESCRT-III proteins are believed to mediate the necessary vesicle extrusion and/or membrane fission activities, possibly in conjunction with the AAA ATPase VPS4. Selectively binds to phosphatidylinositol 3,5-bisphosphate PtdIns(3,5)P2 and PtdIns(3,4)P2 in preference to other phosphoinositides tested. Involved in late stages of cytokinesis. Plays a role in endosomal sorting/trafficking of EGF receptor (By similarity). Probable core component of the endosomal sorting required for transport complex III (ESCRT-III). ESCRT-III components are thought to multimerize to form a flat lattice on the perimeter membrane of the endosome. Several assembly forms of ESCRT-III may exist that interact and act sequentially. Forms a metastable monomer in solution; its core structure (without part of the putative autoinhibitory C-terminal acidic region) oligomerizes into a flat lattice via two different dimerization interfaces. In vitro, heteromerizes with CHMP2A (but not CHMP4) to form helical tubular structures that expose membrane-interacting sites on the outside whereas VPS4B can associate on the inside of the tubule. May interact with IGFBP7; the relevance of such interaction however remains unclear. Interacts with CHMP2A. Interacts with CHMP4A; the interaction requires the release of CHMP4A autoinhibition. Interacts with VPS4A. Interacts with STAMBP; the interaction appears to relieve the autoinhibition of CHMP3 (By similarity). Interacts with VTA1 (By similarity). Localizes to the midbody of dividing cells. Expressed in lung, testis, heart, spleen, skeletal muscle, kidney, liver and brain. The acidic C-terminus and the basic N-termminus are thought to render the protein in a closed, soluble and inactive conformation through an autoinhibitory intramolecular interaction. The open and active conformation, which enables membrane binding and oligomerization, is achieved by interaction with other cellular binding partners, probably including other ESCRT components. Belongs to the SNF7 family.