mRNA selection for translation: beyond the canonical view

生物学的一个中心原则是，在基因DNA中发现的信息被转化为信使RNA分子(MRNA)，然后再转化为一系列氨基酸，称为蛋白质。蛋白质执行大多数生物功能，催化新陈代谢反应，并发挥结构和调节作用。细胞中存在的成熟蛋白质的补体决定了它的身份、功能和健康。因此，对于所有生命来说，细胞有能力控制产生哪些蛋白质、何时产生、产生时的水平以及它们在细胞内的产生位置是至关重要的。细胞中一些最丰富的蛋白质，如参与能量生产和蛋白质本身生产的蛋白质，往往比其他更具调节作用的蛋白质丰富几千倍。这些控制显而易见的一个关键阶段是，生产蛋白质的机器，即核糖体，被招募到RNA中。在过去的50年里，科学家们逐渐拼凑出一条涉及一系列蛋白质因子的途径，这些蛋白质因子在信使核糖核酸的翻译中起着重要作用。最近，他们在其中许多蛋白质中添加了单个分子的精确结构。总体而言，这导致了一个经典的教科书模型，描述了核糖体重新聚集到从酵母到人类细胞的mRNA的过程，被称为翻译起始途径。在我们最近的工作中，我们使用了相对简单的酵母模型系统来问--即使在一个更简单的细胞中，存在的数千个不同的mRNA分子与这些不同的翻译因子相互作用的情况如何？这项工作带来了一个令人惊讶的观察结果。许多产生细胞中最丰富的蛋白质的mRNAs--对生命的基本途径至关重要的蛋白质--与这些翻译因子作用很差。这就引出了一个问题--这些对所有生命系统至关重要的mRNA是如何在其他mRNA的海洋中有效地竞争核糖体的？因此，我们开始研究mRNAs在细胞内的翻译位置。同样，我们惊讶地发现，上面描述的许多基本mRNAs是在特定的站点被翻译的，这些站点被称为“翻译工厂”。在细胞内的特殊位置生产这些蛋白质是有意义的，因为这意味着这个过程可以进行微调和协调，而不会干扰更普遍的蛋白质生产。然而，决定哪些mRNA在当地工厂翻译的规则，以及这些地点翻译过程中涉及的蛋白质因素，人们知之甚少。因此，在这项提议中，我们将确定使基本的大量翻译的mRNAs能够翻译的分子规则。这将包括翻译工厂中涉及的RNA序列和蛋白质因子，这些位点上规范的翻译因子的作用，以及这些机制对细胞生命的重要性。更好地理解细胞如何优先处理被翻译成蛋白质的mRNAs，将立即应用于医疗和商业蛋白质的生产--使有价值的蛋白质能够高水平表达，并将对疾病研究产生影响--从蛋白质聚集在细胞中的疾病，如帕金森氏症，到与缺乏相关的营养疾病，特别是与新陈代谢相关的蛋白质。

A central tenet of biology is that information found in the DNA of genes is converted into a messenger RNA molecule (mRNA), which is then translated into a chain of amino acids called a 'protein'. Proteins carry out most biological functions, catalyzing metabolic reactions as well as serving structural and regulatory roles. The complement of mature proteins present in a cell dictate its identity, function and health. Therefore, it is critical to all life that cells have the capacity to control which proteins are produced, when they are produced, their level when produced and their site of production within the cell. Some of the most abundant proteins in the cell such as proteins involved in the production of energy and in the production of proteins themself are often 1000s of times more abundant than other more regulatory proteins. One key stage where these controls are evident is when the machine for producing proteins, termed the ribosome, is recruited to the RNA. Scientists over the last 50 years have gradually pieced together a pathway involving a series of protein factors that are important in the translation of mRNA. More recently they have added the precise structures of the individual molecules within many of these proteins. Overall, this has led to a canonical textbook model for the process of ribosome recruitment to an mRNA that is conserved from yeast to human cells and is called the translation initiation pathway.In our recent work, we have used the relatively simple yeast model system to ask- how well do the 1000s of different mRNA molecules present even in a simpler cell interact with these different translation factors? This work has led to a surprising observation. Many of the mRNAs producing the most abundant proteins in the cell - proteins critical for fundamental pathways of life - interact poorly with these translation factors. This then begs a question- how do these mRNAs that are fundamental to all living systems effectively compete for ribosomes in a sea of other mRNAs? Hence, we started to look at where mRNAs are translated within cells. Again, we were surprised to find that many of the fundamental mRNAs described above are translated at specific sites that have been termed 'translation factories'. It makes sense to produce these proteins in a special place within the cell, as it means the process can be fine-tuned and co-ordinated without interfering with more general production of proteins. However, the rules that decide which mRNAs are translated in a local factory and the protein factors involved in the translation process in these sites are very poorly understood. Therefore, in this proposal, we will determine the molecular rules that enable translation of fundamental heavily translated mRNAs. This will include the RNA sequences and protein factors involved in translation factories, the role of canonical translation factors at these sites, and the importance of these mechanisms for a cell's life. A greater understanding of how cells prioritise the mRNAs that are translated into protein will have immediate applications in the production of medical and commercial proteins - enabling high level expression of valuable proteins, and will also impact upon studies of disease- from diseases where proteins aggregate in cells such as Parkinson's to nutritional diseases associated with deficiencies in particular proteins involved in metabolism.