Signaling for cell death by Fas/APO1 occurs via a distinct region in its intracellular domain. This region contains a conserved sequence motif, the death domain motif, that is also found in the intracellular domains of the p55 tumor necrosis factor receptor and the low affinity nerve growth factor receptor, as well as in the regulatory domain of the ankyrins. A novel protein that specifically binds to the death domain of Fas/APO1 but not to Fas/APO1 molecules with a loss of function point mutation occurring in lprcg mice was cloned by a two-hybrid screen of a HeLa cells' cDNA library. The cloned protein itself contains a death domain motif, and this region binds to the death domain of Fas/APO1, while the region upstream to the death domain prompts self-association of the protein. Induced expression of the protein results in ligand-independent triggering of cytotoxicity, suggesting that it is involved in cell death induction by Fas/APO1.