Two related proteins, TRAF1 and TRAF2 (TNF receptor-associated factors 1 and 2, respectively), form a heterodimeric complex that associates with the cytoplasmic domain of the tumor necrosis factor (TNF) receptor type 2 (1). A third member of this family, TRAF3 (also designated CD40bp or CRAF1) associates with the cytoplasmic domain of CD40 (2). Additional membersof the TRAF/CRAF family of signaling intermediates include TRAF4 (also designated CART1), TRAF5 and TRAF6 (3-5). TRAF4 associated factor 2 (TRAF4-AF2), also designated sorting nexin 6 (SNX6), is a member of the sorting nexin family of molecules, which are widely expressed and associate with various receptor (6).