PEPTIDES CONTAINING A CONSENSUS RAS BINDING SEQUENCE FROM RAF-1 AND THE GTPASE-ACTIVATING PROTEIN NF1 INHIBIT RAS FUNCTION

A key event in Ras-mediated signal transduction and transformation inv olves Ras interaction with its downstream effector targets. Although s ubstantial evidence has established that the Raf-l serine/threonine ki nase is a critical effector of Ras function, there is increasing evide nce that Ras function is mediated through interaction with multiple ef fecters to trigger Raf-independent signaling pathways. In addition to the two Ras GTPase activating proteins (GAPs; p120- and NF1-GAP), othe r candidate effecters include activators of the Ras-related Ral protei ns (RalGDS and RGL) and phosphatidylinositol 3-kinase. Interaction bet ween Ras and its effecters requires an intact Ras effector domain and involves preferential recognition of active Ras-GTP. Surprisingly, the se functionally diverse effecters lack significant sequence homology a nd no consensus Ras binding sequence has been described. We have now i dentified a consensus Ras binding sequence shared among a subset of Ra s effecters. We have also shown that peptides containing this sequence from Raf-l (RKTFLKCA) and NF1-GAP (RRFFLDIA) block NF1-GAP stimulatio n of Ras GTPase activity and Pas-mediated activation of mitogen-activa ted protein kinases. In summary, the identification of a consensus Ras -GTP binding sequence establishes a structural basis for the ability o f diverse effector proteins to interact with Ras-GTP. Furthermore, our demonstration that peptides that contain Ras-GTP binding sequences ca n block Ras function provides a step toward the development of anti-Pa s agents.