Catalytic domain of the Serine/Threonine Kinases, fungal Byr2-like Mitogen-Activated Protein Kinase Kinase Kinases
STKs catalyze the transfer of the gamma-phosphoryl group from ATP to serine/threonine residues on protein substrates. Members of this group include the MAPKKKs Schizosaccharomyces pombe Byr2, Saccharomyces cerevisiae and Cryptococcus neoformans Ste11, and related proteins. They contain an N-terminal SAM (sterile alpha-motif) domain, which mediates protein-protein interaction, and a C-terminal catalytic domain. MAPKKKs phosphorylate and activate MAPK kinases, which in turn phosphorylate and activate MAPKs during signaling cascades that are important in mediating cellular responses to extracellular signals. Fission yeast Byr2 is regulated by Ras1. It responds to pheromone signaling and controls mating through the MAPK pathway. Budding yeast Ste11 functions in MAPK cascades that regulate mating, high osmolarity glycerol, and filamentous growth responses. The Byr2 subfamily is part of a larger superfamily that includes the catalytic domains of other protein STKs, protein tyrosine kinases, RIO kinases, aminoglycoside phosphotransferase, choline kinase, and phosphoinositide 3-kinase.
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