FIG. 8.

Model of Spa15 function in the eukaryotic cell. Since caspase-3 activation is inhibited in infected cells in the presence of STS, there are three possible mechanisms by which Spa15 could inhibit caspase-3 activation. Spa15 could bind directly to caspase-3 to prevent cleavage and activation (A), inhibit the activated form of caspase-9 to prevent caspase-3 activation (B), or enhance the binding of an IAP to caspase-3 (C). This enhanced binding would prevent Smac/Diablo from dissociating the IAP from caspase-3 and prevent caspase-9 from activating caspase-3.