Catalytic domain of the Serine/Threonine Kinases, Fungal Mitogen-Activated Protein Kinases Sty1 and Hog1
STKs catalyze the transfer of the gamma-phosphoryl group from ATP to serine/threonine residues on protein substrates. This subfamily is composed of the MAPKs Sty1 from Schizosaccharomyces pombe, Hog1 from Saccharomyces cerevisiae, and similar proteins. Sty1 and Hog1 are stress-activated MAPKs that partipate in transcriptional regulation in response to stress. Sty1 is activated in response to oxidative stress, osmotic stress, and UV radiation. It is regulated by the MAP2K Wis1, which is activated by the MAP3Ks Wis4 and Win1, which receive signals of the stress condition from membrane-spanning histidine kinases Mak1-3. Activated Sty1 stabilizes the Atf1 transcription factor and induces transcription of Atf1-dependent genes of the core environmetal stress response. Hog1 is the key element in the high osmolarity glycerol (HOG) pathway and is activated upon hyperosmotic stress. Activated Hog1 accumulates in the nucleus and regulates stress-induced transcription. The HOG pathway is mediated by two transmembrane osmosensors, Sln1 and Sho1. MAPKs are important mediators of cellular responses to extracellular signals. The Sty1/Hog1 subfamily is part of a larger superfamily that includes the catalytic domains of other STKs, protein tyrosine kinases, RIO kinases, aminoglycoside phosphotransferase, choline kinase, and phosphoinositide 3-kinase.
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