Apoptosis-inducing factor(AIF), whose gene lies in X-chromosome, is likely an apoptogenic effector protein to mediates nuclear apoptosis directly. Once synthesized in the cytoplasm, the mouse AIF-precursor preprotein can be effectively imported into the mitochondrial intermembrane space through its N-terminal mitochondrial localization sequence (MLS). Then the MLS is cut off at position Gly 102 of the full-length preprotein, and the remains is refolded and bound with FAD group to produce the apoptogenic mature AIF, with a relative molecular mass of 57 ku. When death stimuli present, AIF is released from mitochondria to the cytoplasm and then to the nucleus, inducing peripheral chromatin condensation and large-scale fragmentation of DNA (～50 kb). These effects cannot be prevented either by the presence of wide-spectrum caspase inhibitor z-VAD.fmkor by the overexpression of Bcl-2. The evidences of gene knockout experiments indicate that AIF is essential for the cavitation of embryoid bodies during mouse morphogenesis, and the cavitation can be caused by AIF itself, independent on caspase-3 activity. Therefore, AIF-mediated cell death maybe constitutes a caspases-independent, more ancient and conserved apoptosis pathway.