Shou C, Farnsworth C L, Neel B G, Feig L A
Department of Biochemistry, Tufts University School of Medicine, Boston, Massachusetts 02111.
Nature. 1992 Jul 23;358(6384):351-4. doi: 10.1038/358351a0.
The stimulation of a variety of cell surface receptors promotes the accumulation of the active, GTP-bound form of Ras proteins in cells. This is a critical step in signal transduction because inhibition of Ras activation by anti-Ras antibodies or dominant inhibitory Ras mutants blocks many of the effects of these receptors on cellular function. To reach the active GTP-bound state, Ras proteins must first release bound GDP. This rate-limiting step in GTP binding is thought to be catalysed by a guanine-nucleotide-releasing factor (GRF). Here we report the cloning of complementary DNAs from a rat brain library that encode a approximately 140K GRF for Ras p21 (p140Ras-GRF). Its carboxy-terminal region is similar to that of CDC25, a GRF for Saccharomyces cerevisiae RAS. This portion of Ras-GRF accelerated the release of GDP from RasH and RasN p21 in vitro, but not from the related RalA, or CDC42Hs GTP-binding proteins. A region in the amino-terminal end of Ras-GRF is similar to both the human breakpoint cluster protein, Bcr, and the dbl oncogene product, a guanine-nucleotide-releasing factor for CDC42Hs. An understanding of Ras-GRF function will enhance our knowledge of the many signal transduction pathways mediated by Ras proteins.
多种细胞表面受体的刺激会促使细胞中活性的、结合GTP的Ras蛋白形式积累。这是信号转导中的关键步骤，因为抗Ras抗体或显性抑制性Ras突变体对Ras激活的抑制会阻断这些受体对细胞功能的许多影响。为了达到活性的结合GTP状态，Ras蛋白必须首先释放结合的GDP。GTP结合中的这一限速步骤被认为是由鸟嘌呤核苷酸释放因子（GRF）催化的。在此，我们报道了从大鼠脑文库中克隆出的互补DNA，其编码一种约140K的Ras p21鸟嘌呤核苷酸释放因子（p140Ras-GRF）。其羧基末端区域与酿酒酵母RAS的鸟嘌呤核苷酸释放因子CDC25相似。Ras-GRF的这一部分在体外加速了GDP从RasH和RasN p21的释放，但未加速从相关的RalA或CDC42Hs GTP结合蛋白的释放。Ras-GRF氨基末端的一个区域与人类断裂点簇蛋白Bcr以及dbl癌基因产物（一种CDC42Hs的鸟嘌呤核苷酸释放因子）都相似。对Ras-GRF功能的了解将增进我们对由Ras蛋白介导的许多信号转导途径的认识。
