Role of the C-terminal domain of Bax and Bcl-x(L) in their localization and function in yeast cells

It has been suggested that the C-terminal domain of Bcl-2 family members ma y contain a signal anchor sequence that targets these proteins to the mitoc hondrial outer membrane. We have investigated the consequence of deleting t his domain upon cytochrome c release in yeast strains that coexpress trunca ted forms of Bas (i.e. Bax Delta) and Bcl-x(L) (i.e. Bcl-x(L)Delta). We fin d that (i) Bax Delta is as efficient as full-length Bat in promoting cytoch rome c release, but Bcl-x(L)Delta has remarkably reduced rescuing ability c ompared to full-length Bcl-x(L); (ii) full-length Bcl-x(L) protein acts by relocalizing Bas from the mitochondrial fraction to the soluble cytosolic f raction; (iii) Bax undergoes N-terminal cleavage when expressed in yeast, w hich is prevented by coexpression of Bcl-x(L), suggesting that Bcl-x(L) mal l mask the cleavage site of Bas through a direct physical interaction of th e two proteins. (C) 1999 Federation of European Biochemical Societies.