THE BCL-2 PROTEIN IS INSERTED INTO THE OUTER-MEMBRANE BUT NOT INTO THE INNER MEMBRANE OF RAT-LIVER MITOCHONDRIA IN-VITRO

The bcl-2 gene encodes a 26 kDa protein, overexpression of which blocks cell apoptosis. Since conflicting data have been reported concerning the localization of the Bcl-2 protein with mitochondrial inner and outer membranes, we analyzed in vitro import of the human Bcl-2 protein into isolated rat liver mitochondria. The Bcl-2 protein translated in rabbit reticulocyte lysate was efficiently inserted into the mitochondrial outer rather than the inner membrane in a membrane potential-independent manner. The carboxyl-terminal hydrophobic stretch is essential for the Bcl-2 protein to integrate into the outer membrane. Binding of the Bcl-2 protein to the mitochondria was not affected by pretreatment of the mitochondria with trypsin, indicating that the Bcl-2 protein does not require protease-sensitive mitochondrial surface components for its membrane insertion. © 1993 Academic Press, Inc.