Osmoregulation and protein expression in a pbs2delta mutant of Saccharomyces cerevisiae during adaptation to hypersaline stress.

We deleted the PBS2 gene encoding the MAP kinase activator of the osmosignaling HOG pathway in Saccharomyces cerevisiae and examined the effects on the kinetics of the osmoregulatory glycerol response and protein induction during adaptation to 0.7 M NaCl. Changes in protein expression as analyzed by two-dimensional polyacrylamide gel electrophoresis (2D PAGE) demonstrated that for the 29 proteins showing a 6-fold induction in wild-type cells during adaptation to NaCl stress, all displayed a decreased and delayed response in pbs2delta cells. Of the seven proteins that were identified, two were previously not known to be under HOG pathway control: Ald6p, an isoform of aldehyde dehydrogenase and Dak1p, a putative dihydroxyacetone kinase. The presence of a remaining significant induction in pbs2delta cells for about half of the examined proteins indicates existence of alternative osmosignaling pathway(s). Northern analysis of the salt induced transcription of GPD1 and GPP2, encoding the cytosolic glycerol-3-phosphate dehydrogenase and glycerol-3-phosphatase involved in the osmostress induced glycerol production, demonstrated an about 20-fold PBS2-dependent transient activation, in agreement with the previously reported transient nature of the signal transduced by the HOG pathway.