Fundamental connections between protein synthesis and carbohydrate metabolism: eIF4A regulation

基因中携带的来自活细胞的信息被解码，产生不同的氨基酸链，称为蛋白质，这些氨基酸链决定了细胞的身份和功能。蛋白质代表了所有生命的基石之一，催化了大多数生物化学反应，并发挥了许多结构和调节作用。基因和蛋白质之间的中间体是信使RNA （mRNA）。在真核细胞（动物、植物和真菌）中，基因已经分离到细胞核中，远离参与蛋白质合成的机制，从而允许mRNA和蛋白质生产的独立调节。mRNA中编码的“翻译”是一个复杂的过程，在真核细胞中高度相似。所有生物都需要能够适应外部环境的变化。这种适应包括改变细胞内单个蛋白质的水平。因此，为了应对诸如温度升高或某些营养物质的饥饿等压力，细胞迅速停止蛋白质合成过程，以允许切换到特定压力的蛋白质生产途径。我们正在用简单的真核生物啤酒酵母作为模式生物来研究这种翻译的调节。糖是生命所必需的。从根本上说，糖的分解提供了驱动活细胞中大多数其他过程的化学能。从细菌到人类，大多数生命系统都将葡萄糖作为主要的能量来源。例如，作为简单的真核微生物，酵母更喜欢以葡萄糖作为糖源生长。在酵母对应激反应中观察到的蛋白质产量最显著的下降之一发生在从生长培养基中消耗葡萄糖后。我们最近发现，一个特定的和关键的翻译因子解离翻译机制后，葡萄糖饥饿。这个因子被称为真核生物翻译起始因子4A （eIF4A）。eIF4A是一类被称为解旋酶的蛋白质的一个例子。这些蛋白质可以解开DNA和RNA分子，eIF4A可以解开mRNA的部分。这被认为使翻译机制能够进入并促进翻译机制沿着mRNA的整体转运或“扫描”，以寻找起始位点。因此，在本提案中，我们将研究从酵母细胞中去除葡萄糖如何导致翻译mrna的eIF4A丢失。我们试图回答以下问题：是什么原因导致与翻译机制相关的eIF4A水平降低，eIF4A缺失对抑制蛋白质产生有多重要，以及继续翻译的mrna是否被eIF4A或其他解旋酶结合。这个项目很重要，因为它汇集了生命系统的两个基本途径，即能量产生系统和蛋白质产生系统。对啤酒酵母中这一机制的详细描述将有助于在其他生物体中进行更长期的研究。如果这种翻译控制途径存在于其他生物体中（可能被不同的胁迫激活），那么它可能对该生物体的生理学非常重要。如果该途径被证明是真菌特异性的，那么它可能代表了对抗人类致病真菌的药物设计的新目标。

The information carried in the genes from living cells is decoded to produce chains of different amino acids called proteins that dictate the identity and function of that cell. Proteins represent one of the building blocks of all life, catalyzing most of the biochemical reactions as well as serving numerous structural and regulatory roles. An intermediate between the gene and the protein is the messenger RNA (mRNA). In eukaryotic cells (animals, plants and fungi), genes have been segregated into the nucleus away from the machinery involved in protein synthesis allowing independent regulation of mRNA and protein production. The 'translation' of the code contained in the mRNA is a complicated process that is highly similar across eukaryotic cells. All organisms need to be able to adapt to changes in their external environment. This adaptation involves changing the levels of individual proteins within cells. Hence, in response to stresses such as increases in temperature or starvation for certain nutrients, cells rapidly halt the process of protein synthesis to allow a switch to a stress specific protein production pathway. We are studying this regulation of translation using the simple eukaryote, brewer's yeast, as a model organism. Sugars are essential for life. Fundamentally, the breakdown of sugars provides the chemical energy that drives most other processes in living cells. The sugar, glucose, is used as the major source of energy in most living systems from bacteria to humans. For instance, as simple eukaryotic micro-organisms, yeast prefer to grow on glucose as a sugar source. One of the most dramatic decreases in protein production observed in response to stress in yeast occurs rapidly after the depletion of glucose from the growth media. We have recently discovered that a specific and critical translation factor dissociates from the translation machinery after glucose starvation. This factor is called the eukaryotic translation initiation factor 4A (eIF4A). eIF4A is an example of a class of proteins called helicases. These proteins can unwind DNA and RNA molecules, and eIF4A can unwind sections of the mRNA. This is thought to give the translation machinery access and promote the overall transit or 'scanning' of this machinery along the mRNA in search of an initiation site.Therefore in this proposal, we will study how the removal of glucose from yeast cells causes a loss of eIF4A from translating mRNAs. We seek to answer questions relating to what causes this reduction in the level of eIF4A associated with the translation machinery, how important this eIF4A loss is in the inhibition of protein production and whether mRNAs that continue to be translated are bound by eIF4A or other helicases. This project is important because it brings together two pathways that are fundamental to living systems these are the energy generating system and the protein production system. A detailed characterisation of this mechanism in brewer's yeast will facilitate the longer term investigation in other organisms. Should such a pathway of translation control be present in other organisms (possibly activated by different stresses) then it is likely to be very important for the physiology of that organism. Should the pathway prove to be fungal-specific then it might represent a new target for drug design to combat human pathogenic fungi.