Daxx was originally identified as a protein factor that binds to a transmembrane receptor called Fas (FAS/APO-1/CD95), one member of the tumor necrosis factor receptor superfamily (Yang et al. 1997). The extracellular region of Fas is where its ligand, FasL, binds. The intracellular tail shares sequence similarity with another member of the TNF receptor family, TNF receptor I (TNFRI). The shared sequence is termed death domain for its critical role in signaling cell death upon ligand binding.