The study investigates the movement of Bax, a member of the Bcl-2 protein family, from the cytosol to mitochondria during apoptosis. Using green fluorescent protein (GFP) fusion constructs, the researchers found that GFP-Bax diffuses throughout the cytosol in healthy cells, while GFP-Bcl-2 and GFP-Bcl-XL colocalize with mitochondrial markers. Upon induction of apoptosis, GFP-Bax redistributes to a punctate distribution that partially colocalizes with mitochondria, a process that occurs within 30 minutes before cellular shrinkage or nuclear condensation. The removal of the COOH-terminal hydrophobic domain from GFP-Bax inhibits this redistribution and reduces its ability to promote cell death. These findings suggest that the redistribution of soluble Bax to organelles is crucial for its pro-apoptotic function.The study investigates the movement of Bax, a member of the Bcl-2 protein family, from the cytosol to mitochondria during apoptosis. Using green fluorescent protein (GFP) fusion constructs, the researchers found that GFP-Bax diffuses throughout the cytosol in healthy cells, while GFP-Bcl-2 and GFP-Bcl-XL colocalize with mitochondrial markers. Upon induction of apoptosis, GFP-Bax redistributes to a punctate distribution that partially colocalizes with mitochondria, a process that occurs within 30 minutes before cellular shrinkage or nuclear condensation. The removal of the COOH-terminal hydrophobic domain from GFP-Bax inhibits this redistribution and reduces its ability to promote cell death. These findings suggest that the redistribution of soluble Bax to organelles is crucial for its pro-apoptotic function.