Inhibitory and activating functions for MAPK Kss1 in the S. cerevisiae filamentous-growth signalling pathway.
Mitogen-activated protein kinase (MAPK) cascades are conserved signalling modules that regulate responses to diverse extracellular stimuli, developmental cues and environmental stresses. A MAPK is phosphorylated and activated by a MAPK kinase (MAPKK), which is activated by an upstream protein kinase, such as Raf, Mos or a MAPKK kinase. Ste7, a MAPKK in the yeast Saccharomyces cerevisiae, is required for two developmental pathways: mating and invasive (filamentous) growth. Kss1 and Fus3, the MAPK targets of Ste7, are required for mating, but their role in invasive growth has been unclear. Because no other S. cerevisiae MAPK has been shown to function in invasive growth, it was proposed that Ste7 may have non-MAPK targets. We show instead that Kss1 is the principal target of Ste7 in the invasive-growth response in both haploids and diploids. We demonstrate further that Kss1 in its inactive form is a potent negative regulator of invasive growth. Ste7 acts to relieve this negative regulation by switching Kss1 from an inhibitor to an activator. These results indicate that this MAPK has a physiologically important function in its unactivated state. Comparison of normal and MAPK-deficient cells indicates that nitrogen starvation and activated Ras stimulate filamentous growth through both MAPK-independent and MAPK-dependent means.
Cook
J G
JG
Department of Molecular and Cell Biology, University of California, Berkeley 94720-3202, USA.
Bardwell
L
L
Thorner
J
J
D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D004789:Enzyme Activation; D005656:Fungal Proteins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D020930:MAP Kinase Kinase Kinases / Q000235:genetics / Q000378:metabolism; D020929:Mitogen-Activated Protein Kinase Kinases; D020928:Mitogen-Activated Protein Kinases; D016296:Mutagenesis; D011494:Protein Kinases / Q000235:genetics / Q000378:metabolism*; D012441:Saccharomyces cerevisiae / Q000201:enzymology* / Q000254:growth & development; D029701:Saccharomyces cerevisiae Proteins; D029702:Schizosaccharomyces pombe Proteins; D015398:Signal Transduction; D014157:Transcription Factors; D018631:ras Proteins / Q000235:genetics / Q000378:metabolism
D005656:Fungal Proteins; D029701:Saccharomyces cerevisiae Proteins; D029702:Schizosaccharomyces pombe Proteins; D014157:Transcription Factors; C071596:ste11 protein, S pombe; D011494:Protein Kinases; D017871:Calcium-Calmodulin-Dependent Protein Kinases; C075580:FUS3 protein, S cerevisiae; C541984:KSS1 protein, S cerevisiae; D020928:Mitogen-Activated Protein Kinases; D020930:MAP Kinase Kinase Kinases; C067018:Ste11 protein, S cerevisiae; D020929:Mitogen-Activated Protein Kinase Kinases; D018631:ras Proteins