Natural causes of programmed death of yeast Saccharomyces cerevisiae.

The existence of cell death program in unicellular organisms has been reported for a number of species. Nevertheless, the question why the ability to commit suicide has been maintained throughout evolution is far from being solved. While it is believed that altruistic death of individual yeast cells could be beneficial for the population, it is generally not known (i) what is wrong with the individuals destined for elimination, (ii) what is the critical value of the parameter that makes a cell unfit and (iii) how the cell monitors this parameter. Studies performed on yeast Saccharomyces cerevisiae allow us to hypothesize on ways of possible solutions of these problems. Here we argue that (a) the main parameter for life-or-death decision measured by the cell is the degree of damage to the genetic material, (b) its critical value is dictated by quorum sensing machinery, and (c) it is measured by monitoring delays in cell division.