The C-terminal end of R-Ras contains a focal adhesion targeting signal.

R-Ras promotes cell adhesion and activation of integrins through a process that is yet unknown. We show here that active R-Ras (38V) promotes the formation of focal adhesions and a spread cell shape. By contrast, the dominant-negative mutant of R-Ras (43N) reduces the number of focal adhesions, leading to the formation of refractile cells. In adherent cells wild-type R-Ras, activated (38V) R-Ras and endogeous R-Ras were preferentially targeted to focal adhesions, whereas the dominant-negative mutant (43N) of R-Ras was excluded from these structures. Activated mutants of H-Ras and K-Ras were not found in focal adhesions. We dissected R-Ras to find out the determinants that are important for the targeting process. The outermost region in the N-terminus of R-Ras, as well as the intact proline-rich sequence in the C-terminus of RRas that mediates binding to Nck, were not essential. Mutating the potential palmitoylation site (C213A) of RRas results in depalmitoylation and accumulation of R-Ras in the Golgi. Using H-Ras/R-Ras, R-Ras/H-Ras and RRas/K-Ras hybrid molecules we showed that the C-termini (175-218 amino acids) of R-Ras contains the signal for focal adhesions targeting. Exchanging the hypervariable region of H-Ras to R-Ras inhibited the targeting of R-Ras to focal adhesions, whereas H-Ras obtained the ability to localize to focal adhesions after receiving the hypervariable region of R-Ras. This indicates that R-Ras targeting is mediated both by the nucleotide binding status as well as through a specific region in the C-terminus of R-Ras. These results indicate that targeting and activation of R-Ras are linked processes in the formation of focal adhesions.