Catalytic domain of fungal Byr1-like dual-specificity Mitogen-activated protein Kinase Kinases
PKs catalyze the transfer of the gamma-phosphoryl group from ATP to serine/threonine (ST) or tyrosine residues on protein substrates. Members of this group include the MAPKKs Byr1 from Schizosaccharomyces pombe, FUZ7 from Ustilago maydis, and related proteins. Byr1 phosphorylates its downstream target, the MAPK Spk1, and is regulated by the MAPKK kinase Byr2. The Spk1 cascade is pheromone-responsive and is essential for sporulation and sexual differentiation in fission yeast. FUZ7 phosphorylates and activates its target, the MAPK Crk1, which is required in mating and virulence in U. maydis. MAPK signaling pathways are important mediators of cellular responses to extracellular signals. The Byr-1 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.