Activation of ras genes in human tumors does not affect localization, modification, or nucleotide binding properties of p21

A comparison of proteins encoded by normal human ras genes and by mutant ras^H or ras^K genes activated in human carcinomas revealed no changes in subcellular localization, posttranslational modification, or guanine nucleotide binding associated with activation. Subcellular fractionation indicated that both normal and activated ras proteins were associated exclusively with the membrane fraction. Furthermore, both normal and activated ras proteins exhibited similar degrees of posttranslational acylation. The K_D for dGTP binding was 1.0-2.2 × 10^-8 M, with no consistent differences between normal and activated ras proteins. In addition, a survey of 13 possible competing nucleotides revealed no differences in the specificity of nucleotide binding associated with ras gene activation. These results indicate that structural mutations which activate ras gene transforming activity do not alter the protein's known biochemical parameters and in particular do not affect the protein's intrinsic ability to bind guanine nucleotides.