Apoptosis is a major form of cell death, characterized by a series of morphological changes induced by cleaving cytoplasmic and nuclear proteins via active caspases. The data presented here show, by fluorescence microscopic and immunoblotting analyses, that a prodomain of caspase-7 inhibits its nuclear translocation and apoptosis-inducing activity. This nuclear localization is dependent on the presence of a basic tetrapeptide that is conserved in mammalian and Xenopus caspase-7 and that is located downstream of a cleavage site between a prodomain and a catalytic protease domain. Furthermore, an attachment of the caspase-7 prodomain (31 amino acids) represses the nuclear transport of a fusion protein of a heterologous protein and the caspase-7 nuclear localization signal (19 amino acids), suggesting that the inhibition of nuclear localization by the prodomain is mediated by the interaction of these short peptides.