Asparagine 26, glutamic acid 31, valine 45, and tyrosine 64 of Ras proteins are required for their oncogenicity.

Ras andRapl proteins are related GTP-dependent signal transducers which require Gly-12, the effector domain (residues 32-40), and Ala-59 for stimulation of their GTPase activities by GAPl and GAP3, respectively.The replacement of Gly-12 by Val or Ala-59 by Thr potentiates the Ras oncogenicity and RaplA antioncogenicity.However, the mutations in the effector domain, in particular the replacement of Thr-35 by Ala, abolish both Ras oncogenicity and RaplA antioncogenicity, indicating that the effector domain is involved in interactions of these signal transducers with their targets as well as the GAPS.In this paper, we demonstrate that (i) replacement of Tyr-64 of the Ha-Ras protein or Phe-64 of the RaplA protein by Glu or other non-hydrophobic amino acids reduces their intrinsic GTPase activities and abolishes their stimulation by GAPl or GAP3, respectively, (ii) replacement of Tyr-64 by Gly and other non-hydrophobic amino acids results in complete loss of the oncogenicity of the v-Ha-Ras protein, indicating that the hydrophobic residue 64, in addition to the known effector domain, is essential for the Ras protein to interact with its target as well as GAP1.In addition we have found that Asn-26, Glu-31, and Val-45 of the v-Ha-Ras protein are required for its oncogenicity.Replacement of the Ras residues at either positions 26, 31, or 45 by the corresponding RaplA residues abolishes the Ras oncogenicity.Mutations in the GTP-binding domains convert normal Ras proteins (Ha, Ki, and N) into highly oncogenic proteins (1).The Rap proteins (lA, lB, 2A, and 2B) share 50% sequence identity with the Ras proteins (2-5), and the RaplA protein potentially reverses the malignant transformation caused by the oncogenically mutated Ras proteins (3).Mutations in the GTP-binding domains also potentiate the anti-Ras action (anti-oncogenicity) of the normal RaplA protein (6).Intrinsic GTPase activities of the Ras and Rapl proteins are stimulated by GAPl and GAP3, respectively (7,8).Since