Hayashizaki S, Iino Y, Yamamoto M
Department of Biophysics and Biochemistry, Graduate School of Science, University of Tokyo, Hongo, Japan.
Genes Cells. 1998 Mar;3(3):189-202. doi: 10.1046/j.1365-2443.1998.00179.x.
The Ras signalling pathway plays several important roles in the development of the nematode Caenorhabditis elegans. So far, two types of Ras-GTPase activating proteins (Ras-GAPs) have been identified in this organism. To aid the study of the regulation and function of the Ras pathway, we set out to isolate a new GAP gene from C. elegans by transcomplementation of the fission yeast gap1 mutant.
We isolated a C. elegans cDNA that encoded a protein which was similar to, but not exactly homologous with mammalian p120 Ras-GAP. This gene, named gap-2, generated at least nine distinct mRNA species through transcription from different promoters and subsequent alternative splicing involving 25 exons. These isoforms were differentially expressed among tissues. A deletion of gap-2 caused no obvious phenotype by itself, but a loss of gap-2 function could suppress larval lethality in both let-23 and let-60 reduction-of-function mutants, in which the Ras activity was lowered.
C. elegans gap-2 encodes a novel Ras-GAP, which is similar to vertebrate p120 but which may constitute a new GAP subfamily. gap-2 mRNA isoforms arise by an unusually extensive variation in initiation sites and associated alternative splicing, and each isoform may play a distinct role in specific tissues. GAP-2 appears to function as a negative regulator of LET-60 Ras during larval development.
Ras信号通路在秀丽隐杆线虫的发育过程中发挥着多种重要作用。到目前为止，在这种生物中已鉴定出两种类型的Ras - GTP酶激活蛋白（Ras - GAPs）。为了有助于研究Ras通路的调控和功能，我们着手通过裂殖酵母gap1突变体的反式互补从秀丽隐杆线虫中分离一个新的GAP基因。
我们分离出一个秀丽隐杆线虫cDNA，其编码的蛋白质与哺乳动物p120 Ras - GAP相似，但并不完全同源。这个名为gap - 2的基因通过从不同启动子转录以及随后涉及25个外显子的可变剪接产生至少九种不同的mRNA种类。这些异构体在不同组织中差异表达。gap - 2的缺失本身并未导致明显的表型，但gap - 2功能的丧失可以抑制let - 23和let - 60功能缺失突变体中的幼虫致死率，在这些突变体中Ras活性降低。
秀丽隐杆线虫gap - 2编码一种新型的Ras - GAP，它与脊椎动物p120相似，但可能构成一个新的GAP亚家族。gap - 2 mRNA异构体通过起始位点的异常广泛变异和相关的可变剪接产生，并且每个异构体可能在特定组织中发挥不同的作用。在幼虫发育过程中，GAP - 2似乎作为LET - 60 Ras的负调节因子发挥作用。
