Apponi Luciano H, Kelly Seth M, Harreman Michelle T, Lehner Alexander N, Corbett Anita H, Valentini Sandro R
Department of Biological Sciences, School of Pharmaceutical Sciences, São Paulo State University, UNESP, Araraquara, SP 14801-902, Brazil.
Mol Cell Biol. 2007 Sep;27(18):6569-79. doi: 10.1128/MCB.00881-07. Epub 2007 Jul 16.
mRNA stability is modulated by elements in the mRNA transcript and their cognate RNA binding proteins. Poly(U) binding protein 1 (Pub1) is a cytoplasmic Saccharomyces cerevisiae mRNA binding protein that stabilizes transcripts containing AU-rich elements (AREs) or stabilizer elements (STEs). In a yeast two-hybrid screen, we identified nuclear poly(A) binding protein 2 (Nab2) as being a Pub1-interacting protein. Nab2 is an essential nucleocytoplasmic shuttling mRNA binding protein that regulates poly(A) tail length and mRNA export. The interaction between Pub1 and Nab2 was confirmed by copurification and in vitro binding assays. The interaction is mediated by the Nab2 zinc finger domain. Analysis of the functional link between these proteins reveals that Nab2, like Pub1, can modulate the stability of specific mRNA transcripts. The half-life of the RPS16B transcript, an ARE-like sequence-containing Pub1 target, is decreased in both nab2-1 and nab2-67 mutants. In contrast, GCN4, an STE-containing Pub1 target, is not affected. Similar results were obtained for other ARE- and STE-containing Pub1 target transcripts. Further analysis reveals that the ARE-like sequence is necessary for Nab2-mediated transcript stabilization. These results suggest that Nab2 functions together with Pub1 to modulate mRNA stability and strengthen a model where nuclear events are coupled to the control of mRNA turnover in the cytoplasm.
mRNA稳定性受mRNA转录本中的元件及其相关RNA结合蛋白的调控。聚尿嘧啶结合蛋白1（Pub1）是一种细胞质酿酒酵母mRNA结合蛋白，可稳定含有富含AU元件（AREs）或稳定元件（STEs）的转录本。在酵母双杂交筛选中，我们鉴定出核聚腺苷酸结合蛋白2（Nab2）是一种与Pub1相互作用的蛋白。Nab2是一种必需的核质穿梭mRNA结合蛋白，可调节聚腺苷酸尾长度和mRNA输出。通过共纯化和体外结合试验证实了Pub1与Nab2之间的相互作用。这种相互作用由Nab2锌指结构域介导。对这些蛋白之间功能联系的分析表明，Nab2与Pub1一样，能够调节特定mRNA转录本的稳定性。RPS16B转录本是一个含有类似ARE序列的Pub1靶标，在nab2-1和nab2-67突变体中其半衰期均缩短。相比之下，含有STE的Pub1靶标GCN4不受影响。对于其他含有ARE和STE的Pub1靶标转录本也获得了类似结果。进一步分析表明，类似ARE的序列是Nab2介导转录本稳定所必需的。这些结果表明，Nab2与Pub1共同发挥作用来调节mRNA稳定性，并强化了一种模型，即核事件与细胞质中mRNA周转的控制相耦合。
