Coordinating different steps in mRNA localization

蛋白质在空间受限模式中的表达经常依赖于编码的先前定位 MRNAs。一种保守的RNA运输机制，用于多种细胞类型，涉及茎环 在信使核糖核酸和蛋白质(平等和双尾-D)内运输信号，以结合信号和连接 携带动力蛋白马达的RNA货物，用于沿微管运输。这一传输系统还将 MRNA在其目的地，尽管对锚定知之甚少。本地化的第一步 果蝇Oskar基因从哺乳细胞到卵母细胞的运输依赖于这种保守的运输 系统。然而，Oskar信使核糖核酸与这个系统的简单例子的不同之处在于，信使核糖核酸必须 转移到不同的本地化机器以进行稍后的本地化步骤。值得注意的是，顺位代理 指导最初运输步骤的Oskar mRNA中的定位信号单独很弱，尽管 交通状况良好。用单个强信号替换多个弱信号会中断后面的步骤 本地化。这表明，与最初运输步骤的机械的弱关联使得 MRNA将被移交给另一种类型的机器。提出了一个模型来解释是什么导致了 奥斯卡交通信号微弱，如何对相互冲突的微弱信号进行高效的要求 交通运输两者都可以满足。在某种程度上，这个模型依赖于Staufen蛋白来抑制卵母细胞的联合 输送机械带有奥斯卡卵母细胞输送信号。Staufen更传统地被认为在 Oskar mRNA本地化的后期步骤，尽管Staufen突变表型与 两款都是。一个目的是用亲和纯化的方法证实奥斯卡依赖于 为其本地化的初始步骤保护交通系统，并揭示其他贡献的候选者 各种因素。第二个目标是测试关于是什么导致个人交通信号微弱的两种预测： 对承认因素的适度亲和力，平等主义；平等主义在 信使核糖核酸进入卵细胞。第三个目的是询问史陶芬对奥斯卡本地化的贡献 信使核糖核酸被限制在这里假设的新角色，或者如果Staufen也具有传统角色，或者两者兼而有之。这个 Staufen的新角色可以解释它是如何促进各种形式的转录后 监管，一种将受到考验的可能性。最终目标是利用该系统的独特功能 敏化遗传分析，以评估候选运输/锚定因素，并筛选这些因素。 对这些因素的进一步分析应该会为mRNA本地化的许多方面提供实质性的见解 然后抛锚。

Expression of proteins in spatially restricted patterns frequently relies on prior localization of the encoding mRNAs. One conserved RNA transport mechanism, used in multiple cell types, involves a stem-loop transport signal within the mRNA, and proteins (Egalitarian and Bicaudal-D) to bind the signal and link the RNA cargo with the dynein motor for transit along microtubules. This transport system also anchors the mRNAs at their destination, although anchoring is poorly understood. The initial step in localization of Drosophila oskar mRNA - transport from the nurse cells to the oocyte - relies on this conserved transport system. However, oskar mRNA differs from simple examples of this system, in that the mRNA must then be transferred to a different localization machinery for a later step in localization. Notably, the cis-acting localization signals in oskar mRNA that direct the initial transport step are individually weak, even though transport is robust. Replacing the multiple weak signals with a single strong signal disrupts the later step in localization. This suggests that weak association with the machinery for the initial transport step allows the mRNA to be handed off to the other type of machinery. A model is proposed to explain what makes the oskar transport signals weak, and how the conflicting requirements for weak signals yet highly efficient transport can both be met. In part, this model relies on Staufen protein to inhibit association of the oocyte transport machinery with the oskar oocyte transport signals. Staufen is more conventionally thought to act in the later step of oskar mRNA localization, although the staufen mutant phenotype is equally consistent with both models. One Aim is to confirm, using an affinity purification approach, that oskar relies on the conserved transport system for its initial step of localization and to reveal candidates for other contributing factors. The second Aim is to test two predictions of what makes the individual transport signals weak: modest affinity for the recognition factor, Egalitarian; and displacement of Egalitarian by Staufen after the mRNA arrives in the oocyte. The third Aim is to ask if the contribution of Staufen to localization of oskar mRNA is limited to the novel role postulated here, or if Staufen also has the conventional role, or both. The novel role for Staufen could explain how it contributes to a wide variety of forms of post-transcriptional regulation, a possibility that will be tested. A final Aim is to exploit unique features of this system in a sensitized genetic assay to evaluate candidate transport/anchoring factors, and to screen for such factors. Further analysis of these factors should provide substantial insights into many aspects of mRNA localization and anchoring.