The beginning and end of poly(A) tails

蛋白质构成了我们细胞的关键组成部分，对确定细胞的身份很重要，它编码在细胞核DNA上的基因中。被称为信使RNA(MRNAs)的部分基因的副本被发送到细胞的细胞质，在那里它们被解码以制造蛋白质。最近的研究表明，当mRNAs在被称为转录的过程中产生时，它们可以被印上一段到期时间，以便通过一种未知的机制在细胞质中移除。有一个已知的信使核糖核酸到期的计时器，即聚(A)尾巴，它通过去除细胞质中的A残基而运行。长期以来，人们一直认为这个定时器(PolyA尾巴的大小)的初始设置几乎总是相同的，mRNAs之间唯一的区别是A残基被CCR4/Not Deadenylase复合体等酶复合体在细胞质中移除的速度有多快。与这一教科书观点相反，我们已经证明了Poly(A)大小的初始设置是在基因开关的过程中在细胞核中调节的，这可以解释mRNA在细胞核中的印记失效时间。我们还表明，核Poly(A)尾巴的大小可以由CCR4/Not Deadenylase复合体调节。值得注意的是，一些非常常见的mRNA在进入细胞质时似乎没有标准的Poly(A)尾巴大小，也没有降低Poly(A)计时器的运行速度，这表明它们的到期受到不同于之前认为的调控。此外，我们还发现两种RNA解旋酶(解旋酶)是CCR4/非相关mRNAs上聚(A)尾的不同调节因子。我们的数据表明，Poly(A)尾巴的产生和移除的方式和位置可能决定其功能。这表明，我们对信使核糖核酸去除的了解并不像我们认为的那么多。为了解决这个问题，我们将使用新的方法来测量数以千计的mRNAs在mRNA生命周期的三个阶段的尾巴大小：当它们在DNA上产生时，就在它们离开细胞核之前和在细胞质中。在一组实验中，我们将移除参与聚(A)尾部调控的蛋白质，包括CCR4/NOT复合体的关键部分和两个解旋酶，并研究其对聚(A)尾部以及对mRNA移除的影响。通过将我们的数据与现有数据相结合，我们将能够了解每个聚(A)尾部调控因子在哪个阶段发挥作用，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，我们将观察自然发生的聚(A)尾巴变化的影响，以检测它们的大小在哪个阶段受到调节，以及这是如何影响它们的稳定性的。我们的工作将回答基本问题，并为这一领域目前的药物开发方案提供信息。

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.