SITE-DIRECTED MUTAGENESIS OF RAS ONCOGENES

我们已经研究了突变型v-ras-H基因的特性，以确定 这些突变对其转化潜力的影响。的 完全转化的v-ras-H基因的表达与 在NIH 3 T3细胞表面MHC表达水平上。某些 突变体转化的细胞显示相对较少的MHC减少，并且这些 突变体在免疫活性小鼠中显示出降低的致瘤性， 形成转移。 我们已经表明，某些非转化突变体，编码p2 l 表现出降低的GTP结合的产品，能够降低 野生型v-ras-H与其他癌基因共转染形成病灶的能力 实验 我们已经分离了一系列的平面回复体（RT）转染后， 将116 Y突变型ras质粒导入v-ras-H转化的3 T3细胞中。RT细胞 表达v-ras-H，与亲本转化细胞相比， 在无血清或血清减少的培养基中较差， 免疫活性小鼠和表达增加水平的MHC I类抗原的 他们的表面。它们在裸鼠体内形成肿瘤的速度减慢， 在培养物中的密度高于未转化的3 T3细胞。RT细胞是 也对蝙蝠ras和mos的再转化具有抗性，这表明它们 代表了一类新的回复突变体。

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.