rRNA degradation depends on the mitochondrial activity in the cell Mitochondria are the major source of endogenous ROS generated by oxidative phosphorylation. The extent to which mitochondria are involved in mammalian or yeast apoptosis is still questionable, although it appears that mitochondrial ROS could be important in some signalling pathways (57,58) and have a central role in some apoptotic pathways and less crucial in others (59) . For example, apoptotic cell death in yeast induced by acetic acid, pheromone and Bax expression was shown to be mediated by mitochondria (31, 60) .