Figure 3.

Model for KSR function. (A) In a quiescent cell, C-Raf, B-Raf, and the inactive KSR/MEK complex are localized in the cytosol, with transient binding interactions occurring between B-Raf and the KSR/MEK complex. (B) Ras activation recruits the Rafs to the plasma membrane where B-Raf participates in C-Raf activation. (C) The KSR/MEK complex also localizes to the membrane and interacts with B-Raf, inducing conformational changes that expose the MEK activation segment for phosphorylation by C-Raf in trans. (D) Inhibitor-induced KSR1/B-Raf complexes can form in the cytosol, thus antagonizing the formation of C-Raf/B-Raf dimers at the membrane.