BID, a BH3 interacting domain death agonist is a member of the Bcl-2/Bcl-xL family. BID can form a heterodimer with either agonist BAX or antagonist Bcl-2. It is a mediator of mitochondrial damage induced by Caspase-8 (CASP8). After the cleavage by CASP8, the COOH-terminal part translocates to mitochondria and induces cytochrome c release, which in turn activates downstream caspases. Multiple alternatively spliced transcript variants have been found, but the full-length nature of some variants has not been defined.