The beginning and end of poly(A) tails

蛋白质是我们细胞的关键组成部分，在确定细胞身份方面很重要，它们编码在细胞核DNA上的基因中。被称为信使RNA（mRNA）的基因部分的拷贝被发送到细胞的细胞质中，在那里它们被解码以产生蛋白质。最近的研究表明，当mRNA在称为转录的过程中产生时，它们可以通过未知的机制在细胞质中被标记有去除的有效时间。mRNA终止有一个已知的计时器，即poly（A）尾，它通过去除细胞质中的A残基而下降。长期以来人们一直认为这个计时器的初始设置（poly（A）尾的大小）实际上总是相同的，mRNA之间的唯一区别在于A残基在细胞质中被酶复合物如CCR 4/NOT去腺苷酶复合物去除的速度。我们已经表明，在基因的开关过程中，poly（A）大小的初始设置在细胞核中受到调节，这可以解释mRNA终止时间在细胞核中的印记。我们还表明，核poly（A）尾的大小可以通过CCR 4/NOT脱腺苷酶复合物调节。引人注目的是，一些非常常见的mRNA在进入细胞质时似乎没有标准的poly（A）尾大小，并且没有耗尽它们的poly（A）计时器，这表明它们的到期受到与以前认为的不同的调节。此外，我们已经确定了两种RNA解旋酶（解旋酶）作为CCR 4/NOT相关mRNA上poly（A）尾的差异调节剂。我们的数据表明，poly（A）尾的产生和去除方式以及位置可能决定其功能。这表明我们对mRNA去除的了解并不像我们想象的那么多。更好地理解poly（A）尾代谢的基本过程对于理解基因在健康生物体以及疾病中的作用至关重要。为了解决这个问题，我们将使用新的方法来测量mRNA生命周期三个阶段中数千种mRNA的poly（A）尾大小：它们在DNA上形成时，就在它们离开细胞核和细胞质之前。在一组实验中，我们将去除参与poly（A）尾调控的蛋白质，包括CCR 4/NOT复合物的关键部分和两个解旋酶，并检查对poly（A）尾以及mRNA去除的影响。通过将我们的数据与现有数据相结合，我们将能够看到每个poly（A）尾调节剂在哪个阶段起作用，以及这如何影响mRNA去除的时间和蛋白质合成的效率。在第二组实验中，我们将研究自然发生的poly（A）尾变化的影响，以检测它们的大小在哪个阶段受到调节以及这如何影响它们的稳定性。我们的工作将回答基本问题，并为该领域的当前药物开发计划提供信息。

Proteins, which form key building blocks of our cells and are important in determining cell identity, are encoded in genes on the DNA in the nucleus of cells. Copies of part of the gene called messenger RNAs (mRNAs) are sent to the cytoplasm of the cell where they are decoded to make the proteins. Recent studies indicate that when mRNAs are made in the process called transcription, they can be imprinted with an expiry time for removal in the cytoplasm by an unknown mechanism. There is a known timer for mRNA expiration, the poly(A) tail, which runs down by removal of the A residues in the cytoplasm. It has long been thought that the initial setting of this timer (the size of the poly(A) tail) was virtually always the same and the only difference between mRNAs was in how quick A residues were removed in the cytoplasm by enzyme complexes such as the CCR4/NOT deadenylase complex.In contrast to this textbook view, we have shown that the initial setting of the poly(A) size is regulated in the nucleus during on and off switching of genes, which could explain the imprinting of an mRNA expiry time in the nucleus. We have also shown that nuclear poly(A) tail size can be regulated by the CCR4/NOT deadenylase complex. Strikingly, some very common mRNAs appear not to have the standard poly(A) tail size when they enter the cytoplasm and don't run down their poly(A) timer, indicating that their expiry is differently regulated than previously thought. Moreover, we have identified two RNA unwinding enzymes (helicases) as differential regulators of poly(A) tails on CCR4/NOT associated mRNAs. Our data suggest that how and where a poly(A) tail is generated and removed may determine its function. It shows that we don't know as much about mRNA removal as we thought we did. A better understanding of the fundamental process of poly(A) tail metabolism is essential for understanding how genes are used in healthy organisms as well as in disease.To address this question, we will use novel methods for measuring poly(A) tail sizes of thousands of mRNAs in three stages of the mRNA life cycle: as they are being made on the DNA, just before they exit the nucleus and in the cytoplasm. In one set of experiments, we will remove proteins involved in poly(A) tail regulation, including a key part of the CCR4/NOT complex and the two helicases and examine the effect on the poly(A) tail as well as on mRNA removal. By combining our data with existing data, we will be able to see in which stage each poly(A) tail regulator works and how this affects the timing of mRNA removal and the efficiency of protein synthesis. In a second set of experiments, we will look at the effects of naturally occuring poly(A) tail changes to detect at which stage their size is regulated and how this affects their stability. Our work will answer fundamental questions as well as inform current drug development programmes in this area.