Abstract: The present invention relates to a fusion protein comprising a Caspase domain or a functionally active variant thereof and a ligand binding domain of a nuclear hormone receptor, a nucleic acid coding for the fusion protein, a vector or cell comprising the nucleic acid, a method of producing the fusion protein, a non-human transgenic animal containing the nucleic acid, the use of the fusion protein for ligand-mediated induction of apoptosis of a cell, or for studying the function of a cell, tissue and/or organ or the use of a transgenic organism for studying the function of a cell at various developmental stages or as a disease model, a method for inducing apoptosis of a cell expressing a fusion protein or for identifying a ligand, or a medicament comprising a fusion protein, the nucleic acid, the vector or the cell, particularly for the treatment of cancer or for or after transplantation, particularly as safety mechanism.