Ras p21 proteins with high or low GTPase activity can efficiently transform NIH 3T3 cells

We sought to determine whether decreased in vitro GTPase activity is uniformly associated with ras p21 mutants possessing efficient transforming properties. Normal H-ras p21-[Gly¹²-Ala⁵⁹] as well as an H-ras p21-[Gly¹²-Thr⁵⁹] mutant exhibited in vitro GTPase activities at least fivefold higher than either H-ras p21-[Lys¹²-Ala⁵⁹] or H-ras p21-[Arg¹²-Thr⁵⁹] mutants. Microinjection of as much as 6 × 10⁶ molecules/cell of bacterially expressed normal H-ras p21 induced no detectable alterations of NIH 3T3 cells. In contrast, inoculation of 4-5 × 10⁵ molecules/cell of each p21 mutant induced morphologic alterations and stimulated DNA synthesis. Moreover, the transforming activity of each mutant expressed in a eukaryotic vector was similar and at least 100-fold greater than that of the normal H-ras gene. These findings establish that activation of efficient transforming properties by ras p21 proteins can occur by mechanisms not involving reduced in vitro GTPase activity.