A putative effector of Ral has homology to Rho/Rac GTPase activating proteins.

We report here the cloning of a gene encoding a novel Ral interacting protein (RIP1) from a cDNA expression library using radiolabeled Ral as probe. RIP1 binds to Ral in a GTP-dependent manner. The 4.1 kb transcript of the RIP1 gene is present in all tissues analysed and encodes for a protein product of 648 residues. RIP1 shares sequence similarity with GAP proteins that are capable of activating the GTPase activity of members of the Rho/Rac family of GTPases. When tested, RIP1 could activate the GTPase activity of CDC42 and, to a lesser extent, Rac1 but not RhoA, Ras, or Ral. Activated Ral had no effect on the GTPase-activating ability of RIP1, in vitro.