HUMAN BAK INDUCES CELL-DEATH IN SCHIZOSACCHAROMYCES-POMBE WITH MORPHOLOGICAL-CHANGES SIMILAR TO THOSE WITH APOPTOSIS IN MAMMALIAN-CELLS

Apoptosis as a form of programmed cell death (PCD) in multicellular or ganisms is a well-established genetically controlled process that lead s to elimination of unnecessary or damaged cells. Recently, PCD has al so been described for unicellular organisms as a process for the socia lly advantageous regulation of cell survival, The human Bcl-2 family m ember Bak induces apoptosis in mammalian cells which is counteracted b y the Bcl-x(L) protein. We show that Bak also kills the unicellular fi ssion yeast Schizosaccharomyces pombe and that this is inhibited by co expression of human Bcl-x(L). Moreover, the same critical BH3 domain o f Bak that is required for induction of apoptosis in mammalian cells i s also required for inducing death in yeast. This suggests that Bak ki lls mammalian and yeast cells by similar mechanisms. The phenotype of the Bak-induced death in yeast involves condensation and fragmentation of the chromatin as well as dissolution of the nuclear envelope, all of which are features of mammalian apoptosis. These data suggest that the evolutionarily conserved metazoan PCD pathway is also present in u nicellular yeast.