Receptor interacting protein including RIP and RIP2/RICK mediate apoptosis induced by TNFR1 and Fas, two prototype members in the death receptor family. A novel member in the RIP kinase family was recently identified and designated RIP3. RIP3 contains N-terminal kinase domain but, unlike RIP or RIP2, lacks the c-terminal death or CARD domain. RIP3 binds to RIP and TNFR1, and mediates TNF-R1 mediated apoptosis, and attenuates RIP and TNFR1 induced NFkB activation. Overexpression of RIP3 induces apoptosis and NFkB activation.