SITE-DIRECTED MUTAGENESIS OF RAS ONCOGENES

我们已经研究了突变的v-ras-H基因的性质，以确定 这些突变对其转化潜力的影响。这个 完全转化的v-ras-H基因的表达与减少相关 NIH3T3细胞表面MHC的表达水平。一定的 突变转化的细胞表现出相对较小的MHC减少，并且这些 突变体显示免疫活性小鼠的致瘤性降低，但未能 形成转移。 我们已经证明了某些非转化突变体，它们编码p21 具有减少的GTP绑定的产品能够减少 Wt v-ras-H等癌基因在共转染中的成灶能力 实验。 我们已经分离出一系列的平坦反转体(RT)。 将116Y突变型ras质粒导入v-ras-H转化3T3细胞。RT细胞 表达v-ras-H，并与亲本转化细胞相比，生长 在无血清或低血清介质中不佳，不能在 并在小鼠体内表达MHC-I类抗原水平升高 它们的表面。它们在裸鼠体内形成肿瘤的速度较慢，并生长到 培养的3T3细胞密度高于未转化的3T3细胞。RT细胞是 也抵抗BAT RAS和MOS的再转化，这表明他们 代表了一类新的返回体。

We have studied the properties of mutant v-ras-H genes to determine the effects of these mutations on their transformation potential. The expression of fully transforming v-ras-H genes correlates with a reduction in the level of MHC expression on the surface of NIH3T3 cells. Certain mutant transformed cells show relatively little MHC reduction, and these mutants show reduced tumorigenicity in immunocompetent mice and fail to form metastases. We have shown that certain non-transforming mutants, which encode a p2l product exhibiting reduced GTP binding, are able to reduce the focus-forming ability of wt v-ras-H and other oncogenes in cotransfection experiments. We have isolated a series of flat revertants (RT) following transfection of the 116Y mutant ras plasmid into v-ras-H transformed 3T3 cells. RT cells express v-ras-H and, in comparison to the parental transformed cells, grow poorly in serum-free or reduced serum media, fail to form tumors in immunocompetent mice and express increased levels of MHC class I antigen on their surfaces. They form tumors in nude mice at reduced rates and grow to higher densities in culture than non-transformed 3T3 cells. RT cells are also resistant to retransformation by bat ras and mos, suggesting that they represent a novel class of revertants.