I. Samejima et al., MULTIPLE-MODES OF ACTIVATION OF THE STRESS-RESPONSIVE MAP KINASE PATHWAY IN FISSION YEAST, EMBO journal, 16(20), 1997, pp. 6162-6170
The Schizosaccharomyces pombe wis1(+) gene is essential for cell survi
val under stress conditions. The MAPKK homologue Wis1 is required for
activation of the MAPK homologue Spc1, and integrity of the Wis1-Spc1
pathway is required for survival in extreme conditions of heat, osmola
rity, oxidation or limited nutrition, We show here that Wis4, a protei
n kinase of a new MAPKKK class, phosphorylates Wis1 in vitro and activ
ates it in vivo, Win1 is also required for full activation of Wis1, an
d Win1 rather than Wis4 mediates the osmotic stress signal. Surprising
ly, the pathway can still be activated by heat or oxidative stress ind
ependently of the phosphorylation of two conserved Wis1 residues, Evid
ence is presented that the Pyp1 protein tyrosine phosphatase, which de
phosphorylates Spc1, is central to this alternative activation mechani
sm.