LARP4 mRNA codon-tRNA match contributes to LARP4 activity for ribosomal protein mRNA poly(A) tail length protection.
LARP4 mRNA codon-tRNA match contributes to LARP4 activity for ribosomal protein mRNA poly(A) tail length protection.
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DOI：
10.7554/elife.28889
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发表时间：
2017-09-12
期刊：
影响因子：
7.7
通讯作者：
Maraia RJ
中科院分区：
文献类型：
--
作者：
Mattijssen S;Arimbasseri AG;Iben JR;Gaidamakov S;Lee J;Hafner M;Maraia RJ
信使RNA的功能由3' poly（A）tail（PAT）和poly（A）-binding protein（PABP）控制。La相关蛋白-4（LARP 4）结合poly（A）和PABP。LARP 4 mRNA含有限制其表达的不稳定性的依赖于抑制的编码区决定簇（CRD）。尽管CRD包含<10%的LARP 4密码子，但mRNA水平随着适应tRNA动力学的同义CRD取代而变化>20倍。单独地，最限制性tRNA的过表达增加LARP 4水平并揭示其功能活性，异源mRNA的PAT的净延长伴随稳定，包括核糖体蛋白（RP）mRNA。细胞LARP 4的遗传缺失降低PAT长度和RPmRNA稳定性。这种LARP 4活性需要其PABP相互作用结构域和RNA结合模块，我们显示其对poly（A）3 '-末端敏感，与保护免于去腺苷化一致。结果表明LARP 4是哺乳动物细胞中核糖体蛋白产生的转录后调节因子，并表明该活性可由tRNA水平控制。基因是编码指令，用于构建构成生物体的蛋白质和其他分子。为了构建蛋白质，基因中的代码被复制到称为信使RNA（或mRNA短）的分子中。然后，遗传密码的字母被称为核糖体的分子机器以三个一组的方式读取，称为密码子。每个密码子对应于所有蛋白质的一个组成部分，称为氨基酸。然而，由于蛋白质中有64种可能的密码子，但只有20种左右的氨基酸，不同的密码子可以编码相同的氨基酸。除了决定蛋白质中氨基酸的顺序，mRNA中的密码子序列也可以有其他影响。一些序列改变mRNA与其他分子结合的方式，而另一些序列则影响mRNA在被分解之前在细胞内持续的时间。事实上，mRNA的稳定性是控制基因活性的重要方式，编码不稳定mRNA的基因通常产生较少的蛋白质。了解DNA密码的全部信息潜力是许多生物学家的主要目标。这一领域的许多研究都集中在单细胞生物如酵母上，但酵母中mRNA的调控通常不如人类复杂。Mattijssen等人现在已经询问了一种称为LARP 4的人类蛋白质的mRNA中的密码子如何影响mRNA的稳定性。这种蛋白质与mRNA分子结合，实验发现了一小段使LARP 4 mRNA非常不稳定的密码子。用相同氨基酸的其他密码子替换该片段中的特定密码子，导致LARP 4 mRNA的稳定性大大增加。这反过来又改变了LARP 4蛋白的产生量。氨基酸被称为转移RNA（或简称tRNA）的分子带到相应的密码子中。Mattijssen等人发现，导致不稳定的LARP 4 mRNA短片段中的密码子与罕见的tRNA相匹配。增加这些低水平tRNA的水平也增加了LARP 4蛋白的产生量。LARP 4水平的升高揭示了该蛋白质的新活性。几乎所有的mRNA在一端都有一个所谓的poly-A尾，实验表明LARP 4与一系列mRNA结合，以帮助使这些尾更长，从而使分子更稳定。从小鼠细胞中删除LARP 4基因会导致原本稳定的mRNA具有较短的poly（A）尾，变得不那么稳定。这包括编码构成核糖体的蛋白质的mRNA。编码核糖体蛋白的mRNA的调节一直是理解的挑战。这些新结果可能揭示了一个信号网络，该网络将细胞中tRNA的数量与核糖体的产生联系起来。由于核糖体的产生是控制细胞生长和分裂的核心，这些结果可能对人类发育和癌症等不同领域的研究产生广泛的影响。
Messenger RNA function is controlled by the 3' poly(A) tail (PAT) and poly(A)-binding protein (PABP). La-related protein-4 (LARP4) binds poly(A) and PABP. LARP4 mRNA contains a translation-dependent, coding region determinant (CRD) of instability that limits its expression. Although the CRD comprises <10% of LARP4 codons, the mRNA levels vary >20 fold with synonymous CRD substitutions that accommodate tRNA dynamics. Separately, overexpression of the most limiting tRNA increases LARP4 levels and reveals its functional activity, net lengthening of the PATs of heterologous mRNAs with concomitant stabilization, including ribosomal protein (RP) mRNAs. Genetic deletion of cellular LARP4 decreases PAT length and RPmRNA stability. This LARP4 activity requires its PABP-interaction domain and the RNA-binding module which we show is sensitive to poly(A) 3'-termini, consistent with protection from deadenylation. The results indicate that LARP4 is a posttranscriptional regulator of ribosomal protein production in mammalian cells and suggest that this activity can be controlled by tRNA levels. Genes are coded instructions to build proteins and other molecules that make up living organisms. To build a protein, the code within a gene is copied into a molecule called a messenger RNA (or mRNA short). The letters of the genetic code are then read in groups of three, referred to as codons, by a molecular machine called a ribosome. Each codon corresponds to one of the building blocks of all proteins, known as amino acids. However, because there are 64 possible codons but only 20 or so amino acids found in proteins, different codons can encode for the same amino acid. In addition to determining the order of amino acids in a protein, the sequence of codons in an mRNA can have other effects too. Some sequences change how the mRNA binds with other molecules, while others affect how long the mRNA will last within the cell before it is broken down. In fact, the stability of an mRNA is an important way to control a gene’s activity and genes that encode unstable mRNAs typically yield less protein. Understanding the full information potential of the DNA code is a major goal of many biologists. Much research in this field has focused on single-celled organisms such as yeast, yet the regulation of mRNAs in yeast is generally less complex than it is in humans. Mattijssen et al. have now asked how codons within the mRNA for a human protein called LARP4 affect the mRNA’s stability. This protein binds to mRNA molecules, and the experiments uncovered a short segment of codons that made the mRNA of LARP4 very unstable. Replacing specific codons in this segment with other codons for the same amino acid caused the stability of the LARP4 mRNA to increase a lot. This in turn changed how much LARP4 protein was produced. Amino acids are brought to their corresponding codons by molecules called transfer RNAs (or tRNAs for short). Mattijssen et al. found that the codons in the short segment of LARP4 mRNA that caused instability were matched by rare tRNAs. Increasing the levels of these low level tRNAs also increased how much LARP4 protein was produced. The elevated levels of LARP4 revealed a new activity for the protein. Almost all mRNAs have a so-called poly-A tail at one end, and the experiments showed that LARP4 binds to a range of mRNAs to help make these tails longer, which in turn makes the molecules more stable. Deleting the gene for LARP4 from mouse cells lead otherwise stable mRNAs to have shorter poly(A) tails and to become less stable. This includes the mRNAs that code for the proteins that make up ribosomes. The regulation of the mRNAs that encode ribosomal proteins has been challenging to understand. These new results may reveal a network of signals that connects the amount of tRNAs in a cell to the production of ribosomes. Since ribosome production is central to controlling cell growth and division, these results may have broad implications in research into areas as varied as human development and cancer.