When ectopically expressed in animal cells, cytokine response modifier A (CrmA), a product
of the cowpox virus, prevents programmed cell death initiated by a variety of stimuli. Since
CrmA is a proteinase inhibitor, its target is probably a protease that promotes cell death. The
identification of this target is crucial in delineating essential regulation points that modulate
the apoptotic program. We have compared the kinetics of interaction of CrmA with five
proteases that may play a role in apoptosis. Four of the proteases, all members of the …