Involvement of B-Raf in Ras-induced Raf-1 activation

The mechanism of Ras-induced Raf-1 activation is not full), understood. Previously, we identified a 400-kDa protein complex as a Ras-dependent Raf-1 activator. In this study, we identified B-Raf as a component of this complex. B-Raf was concentrated during the purification of the activator. linamunodepletion of B-Raf abolished the effect of the activator on Raf-1. Furthermore, B-Raf and Ras-activated Raf-I co-operatively, when co-transfected into human embryonic kidney 293 cells. On the other hand, Ras-dependent extracellular signal-regulated kinase/mitogen-activated protein kinase kinase stimulator (a complex of B-Raf and 14-3-3) failed to activate Raf-I in our cell-free system. These results suggest that B-Raf is an essential component of the Ras-dependent Raf-I activator. Oc 2001 Published by Elsevier Science B.V. on behalf of the Federation of European Biochemical Societies.