Fas-associating death domain containing protein (FADD), also known as mediator of receptor induced toxicity (MORT1), is a 24 kDa cytosolic protein. The protein is involved in both Fas and TNF-R induced cell death pathway. FADD specifically binds to Fas, an association mediated by their homologous death domains. Overexpression of FADD induces apoptosis that can be inhibited by CrmA, a poxvirus protein that blocks both Fas- and TNF-induced cell death.