A novel mitochondrial septin-like protein, ARTS, mediates apoptosis dependent on its P-loop motif

Here we describe a protein product of the human septin H5/PNUTL2/CDCrel2b g ene, which we call ARTS (for apoptosis-related protein in the TGF-beta sign alling pathway). ARTS is expressed in many cells and acts to enhance cell d eath induced by TGF-beta or, to a lesser extent, by other apoptotic agents. Unlike related septin gene products, ARTS is localized to mitochondria and translocates to the nucleus when apoptosis occurs. Mutation of the P-loop of ARTS abrogates its competence to activate caspase 3 and to induce apopto sis. Taken together, these observations expand the functional attributes of septins previously described as having roles in cytokinesis and cellular m orphogenesis.