Hoshino S, Imai M, Kobayashi T, Uchida N, Katada T
Department of Physiological Chemistry, Graduate School of Pharmaceutical Sciences, University of Tokyo, Tokyo 113-0033, Japan.
J Biol Chem. 1999 Jun 11;274(24):16677-80. doi: 10.1074/jbc.274.24.16677.
The mammalian GTP-binding protein GSPT, whose carboxyl-terminal sequence is homologous to the eukaryotic elongation factor EF1alpha, binds to the polypeptide chain releasing factor eRF1 to function as eRF3 in the translation termination. The amino-terminal domain of GSPT was, however, not required for the binding. Search for other GSPT-binding proteins in yeast two-hybrid screening system resulted in the identification of a cDNA encoding polyadenylate-binding protein (PABP), whose amino terminus is associating with the poly(A) tail of mRNAs presumably for their stabilization. The interaction appeared to be mediated through the carboxyl-terminal domain of PABP and the amino-terminal region of GSPT. Interestingly, multimerization of PABP with poly(A), which is ascribed to the action of its carboxyl-terminal domain, was completely inhibited by the interaction with the amino-terminal domain of GSPT. These results indicate that GSPT/eRF3 may play important roles not only in the termination of protein synthesis but also in the regulation of mRNA stability. Thus, the present study is the first report showing that GSPT/eRF3 carries the translation termination signal to 3'-poly(A) tail ubiquitously present in eukaryotic mRNAs.
哺乳动物的GTP结合蛋白GSPT，其羧基末端序列与真核延伸因子EF1α同源，它与多肽链释放因子eRF1结合，在翻译终止过程中发挥eRF3的作用。然而，GSPT的氨基末端结构域对于这种结合并非必需。在酵母双杂交筛选系统中寻找其他与GSPT结合的蛋白，结果鉴定出一个编码聚腺苷酸结合蛋白（PABP）的cDNA，其氨基末端与mRNA的聚（A）尾结合，可能是为了稳定mRNA。这种相互作用似乎是通过PABP的羧基末端结构域和GSPT的氨基末端区域介导的。有趣的是，PABP与聚（A）的多聚化（归因于其羧基末端结构域的作用）被与GSPT氨基末端结构域的相互作用完全抑制。这些结果表明，GSPT/eRF3可能不仅在蛋白质合成终止中发挥重要作用，还在mRNA稳定性的调节中发挥作用。因此，本研究是首次报道表明GSPT/eRF3将翻译终止信号传递给真核mRNA中普遍存在的3'-聚（A）尾。
