OSMOSTRESS RESPONSE OF THE YEAST SACCHAROMYCES

Exposure of yeast cells to high osmolarities leads to dehydration, col lapse of ion gradients over the plasma membrane and decrease in cell v iability. The response of yeast cells to high external osmolarities is designated osmostress response. It is likely that both osmoregulatory and general stress reactions are involved in this so far poorly under stood process. Part of the response aims at raising the internal osmot ic potential, i.e. the production of osmolytes such as glycerol, and e xclusion of toxic solutes. In addition, heat-shock proteins and trehal ose are synthesized, probably to protect cellular components and to fa cilitate repair and recovery. Recent analyses of osmosensitive yeast m utants strongly suggest the involvement of protein kinase-mediated sig nal-transduction pathways in the maintenance of the osmotic integrity of the cell. This has stimulated interesting hypotheses as to the actu al osmosensing mechanism.