A cytochrome c-GFP fusion is not released from mitochondria into the cytoplasm upon expression of Bax in yeast cells

To study Bas-induced release of cytochrome c in vivo, we have expressed a c ytochrome c-GFP (green fluorescent protein) fusion in Saccharomyces cerevis iae cells null for the expression of the endogenous cytochrome. Wr show her e that cytochrome c-GFP is efficiently localised to mitochondria and able t o function as an electron carrier between complexes III and IV of the respi ratory chain. Strikingly, while natural cytochrome c is released into the c ytoplasm upon expression of Bas, the cytochrome c-GFP fusion is not. Nevert heless, cells co-expressing Bax and the cytochrome c-GFP fusion die, indica ting that mitochondrial release of cytochrome c is not essential for cell d eath to occur in yeast. The failure to release cytochrome c-GFP is presumed to arise from increased bulk due to the GFP moiety. We propose that in int act yeast cells, Bax-induced release of cytochrome c into the cytoplasm occ urs through a selective pore and not as a consequence of the non-specific b reakage of the mitochondrial outer membrane. (C) 2000 Federation of Europea n Biochemical Societies.