Induction of apoptosis by Drosophila reaper, hid and grim through inhibition of IAP function

Induction of apoptosis in Drosophila requires the activity of three closely linked genes, reaper, hid and grim. Here we show that the proteins encoded by reaper, hid and grim activate cell death by inhibiting the anti-apoptot ic activity of the Drosophila IAP1 (diap1) protein. In a genetic modifier s creen, both loss-of-function and gain-of-function alleles in the endogenous diap1 gene were obtained, and the mutant proteins were functionally and bi ochemically characterized. Gain-of-function mutations in diap1 strongly sup pressed reaper-, hid- and grim-induced apoptosis. Sequence analysis of thes e alleles revealed that they were caused by single amino acid changes in th e baculovirus IAP repeat domains of diap1, a domain implicated in binding R EAPER, HID and GRIM. Significantly, the corresponding mutant DIAP1 proteins displayed greatly reduced binding of REAPER, HID and GRIM, indicating that REAPER, HID and GRIM kill by forming a complex with DIAP1. These data prov ide strong in vivo evidence for a previously published model of cell death regulation in Drosophila.