| The Raf kinases are important intermediates in signal transduction pathways. Raf-1, the prototype member of this gene family, is a 72-76 kDa cytoplasmic protein with intrinsic serine/threonine kinase activity, is broadly expressed in many cell types and is the cellular homolog of the viral oncogene, v-Raf. Other members of the Raf gene family include Raf-A and Raf-B. Raf-1 phosphorylates and thereby activates MEK (also designated MAP kinase kinase). Ras proteins bind Raf-1, but only when Ras is in its active GTP-binding state. This interaction results in Raf-mediated MEK activation. Two more recently described Raf-related proteins, Ksr-1 and Tak1 (TGF-beta-activated kinase), function as upstream regulators of Ras signaling pathways. |
