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Catalytic domain of the Serine/Threonine Kinases, Raf (Rapidly Accelerated Fibrosarcoma) kinases STKs catalyze the transfer of the gamma-phosphoryl group from ATP to serine/threonine residues on protein substrates. Raf kinases act as mitogen-activated protein kinase kinase kinases (MAP3Ks, MKKKs, MAPKKKs), which phosphorylate and activate MAPK kinases (MAPKKs or MKKs or MAP2Ks), which in turn phosphorylate and activate MAPKs during signaling cascades that are important in mediating cellular responses to extracellular signals. They function in the linear Ras-Raf-MEK-ERK pathway that regulates many cellular processes including cycle regulation, proliferation, differentiation, survival, and apoptosis. Aberrant expression or activation of components in this pathway are associated with tumor initiation, progression, and metastasis. Raf proteins contain a Ras binding domain, a zinc finger cysteine-rich domain, and a catalytic kinase domain. Vertebrates have three Raf isoforms (A-, B-, and C-Raf) with different expression profiles, modes of regulation, and abilities to function in the ERK cascade, depending on cellular context and stimuli. They have essential and non-overlapping roles during embryo- and organogenesis. Knockout of each isoform results in a lethal phenotype or abnormality in most mouse strains. The Raf 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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