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 X 10(6) molecules/cell of bacterially expressed normal H-ras p21 induced no detectable alterations of NIH/3T3 cells. In contrast, inoculation of 4-5 X 10(5) 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.