Several serine / threonine protein kinases have been implicated as intermediates in signal transduction pathways. These include ERK / MAP kinases, ribosomal S6 kinase (Rsk) and Raf-1. Raf-1 is a protein with intrinsic kinase activity towards serine / threonine residues and Which is expressed expression in many human types and cell lines. Raf-1 activation is dependent on the small molecular weight GTPase Ras, but the means by which this activation is poorly understood. Two proteins put put involved in this process are Ksr-1 and Taks. Ksr-1 (kinase sup-pressor of Ras) is a novel Raf-related protein kinase whose function is required for Ras signal transduction. Whether or not in a parallel pathway is not yet known. Tak1 (TGFβ-activated kinase) has been shown to participate in the activation of the MAP kinase family in response to TGFβ stimulation.
