UBAP1 is a component of an endosome-specific ESCRT-I complex that is essential for MVB sorting.
Stefani F, Zhang L, Taylor S, Donovan J, Rollinson S, Doyotte A, Brownhill K, Bennion J, Pickering-Brown S, Woodman P. Curr Biol. 2011 Jul 26; 21(14):1245-50. Epub 2011 Jul 14.