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The structure and function of a novel G protein family regulating eukaryotic mRNA dynamics

调节真核mRNA动态的新型G蛋白家族的结构和功能

基本信息

批准号：
13854025
负责人：
KATADA Toshiaki
金额：
$ 78.87万
依托单位：
The University of Tokyo
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (S)
财政年份：
2001
资助国家：
日本
起止时间：
2001 至 2005
项目状态：
已结题

项目摘要

In eukaryotic protein synthesis, all three termination codons are directly recognized by a polypeptide-chain releasing factor, eRF1,to release polypeptide chain from ribosome, and another releasing factor, eRF3,is required for eRF1 binding to ribosomal A site. We previously reported that a GTP-binding protein, whose carboxy-terminal sequence is homologous to the eukaryotic elongation factor EF1α, forms a complex with eRF1 to function as eRF3 in the translation termination and that eRF3 consists of the EF1α-like carboxy-terminal (C) and amino-terminal (N) domains. In the present studies, we investigated the structures and functions of eRF3 and its related G proteins. The major findings obtained in this study are summarized as follows.1)The C domain of eRF3 associated with eRF1,whereas the N domain was capable of binding to poly-adenylate binding protein (PABP) associating with the poly(A) tail of mRNAs presumably for their stabilization. 2)When the interaction between eRF3-N domain and PABP was abolished, decay rate of all mRNAs was decreased due to the inhibition of poly(A) tail shortening. 3)We identified a poly(A) nuclease (PAN) complex that is activated by PABP and found that eRF3 and PAN complex competitively bound to PABP. These results indicate that the translation termination-coupled mRNA decay is mediated through eRF3-dependent poly(A) shortening. Thus, eRF3 functions not only as an eRF1-carrier protein in the translation termination but also as an initiator of the mRNA degradation machinery. 4)We also investigated the functions of other G proteins (Ski7 and eRFS) structurally related to eRF3 and found that the N domains of these G proteins commonly interact with factors involved in mRNA-degradation machineries to regulate mRNA stabilization.

在真核蛋白合成中，这三个终止密码子都直接被一个多肽链释放因子eRF1识别，从而将多肽链从核糖体中释放出来，而eRF1结合到核糖体a位点则需要另一个释放因子eRF3。我们之前报道了一种gtp结合蛋白，其羧基末端序列与真核延伸因子EF1α同源，与eRF1形成复合物，在翻译末端起eRF3的作用，eRF3由类似EF1α的羧基末端(C)和氨基末端(N)结构域组成。在本研究中，我们研究了eRF3及其相关G蛋白的结构和功能。本研究的主要发现总结如下：1) eRF3的C结构域与eRF1相关，而N结构域能够结合与mrna聚(A)尾部相关的聚腺苷酸结合蛋白（PABP），可能是为了稳定mrna。2)当eRF3-N结构域与PABP之间的相互作用被取消时，由于poly(A)尾巴缩短的抑制，所有mrna的衰减率都降低了。3)我们发现了一个被PABP激活的聚(a)核酸酶（PAN）复合物，并发现eRF3和PAN复合物与PABP竞争性结合。这些结果表明，翻译终止耦合的mRNA衰减是通过erf3依赖性聚(A)缩短介导的。因此，eRF3不仅在翻译终止中作为erf1载体蛋白，而且作为mRNA降解机制的启动者。4)我们还研究了与eRF3结构相关的其他G蛋白（Ski7和eRFS）的功能，发现这些G蛋白的N结构域通常与mRNA降解机制相关的因子相互作用，以调节mRNA的稳定。