In response to many apoptotic stimuli, oligomerization of Bax is essential for 
mitochondrial outer membrane permeabilization and the ensuing release of 
cytochrome c. These events are accompanied by mitochondrial fission that appears 
to require Drp1, a large GTPase of the dynamin superfamily. Loss of Drp1 leads 
to decreased cytochrome c release by a mechanism that is poorly understood. Here 
we show that Drp1 stimulates tBid-induced Bax oligomerization and cytochrome c 
release by promoting tethering and hemifusion of membranes in vitro. This 
function of Drp1 is independent of its GTPase activity and relies on arginine 
247 and the presence of cardiolipin in membranes. In cells, overexpression of 
Drp1 R247A/E delays Bax oligomerization and cell death. Our findings uncover a 
function of Drp1 and provide insight into the mechanism of Bax oligomerization.