Cryo-EM analysis of ribosomal frameshifting

细胞蛋白编码在细胞的遗传物质DNA中，并通过从DNA复制的信使RNA来表达。这个表达过程包括读取三联体核苷酸密码并将其翻译成氨基酸聚合物，即蛋白质。翻译过程涉及一种叫做核糖体的结构。它们沿着信使RNA移动，解码三胞胎，并为每个三胞胎添加一个氨基酸到正在生长的氨基酸链中。感染细胞的病毒携带自己的遗传物质，偶尔会制造信使rna，其中包含一种特定的信号（称为移码信号），该信号告诉核糖体停止制造一种三联体，并开始制造另一种三联体。结果是一个信使RNA可以制造两种蛋白质。这是典型的病毒；由于它们自己的遗传物质通常相对较少，它们使用各种各样的技巧来最大限度地增加它们所能制造的蛋白质的数量。在这个项目中，我们希望研究核糖体遇到移码信号时会发生什么。问题是，核糖体发生了什么使其行为失常？为了回答这个问题，我们将通过移码信号纯化在翻译过程中捕获的核糖体，并通过显微镜研究它们。我们将使用的显微镜技术是基于电子而不是光，因此非常强大，被称为低温电子显微镜。它是“冷冻”的，因为样品在检测前被冷冻在水溶液中，以保持它们处于自然和稳定的状态。我们获得的图像将有望告诉我们一些关于移码信号如何干扰核糖体的信息，也应该提供关于核糖体在正常蛋白质合成过程中如何工作的信息。

Cell proteins are encoded in DNA, the cell's genetic material, and expressed from so-called messenger RNA copied from DNA. This process of expression involves reading a triplet nucleotide code and translating it into an amino acid polymer, the protein. The process of translation involves structures called ribosomes. These move along the messenger RNA decoding the triplets and adding one amino acid for each triplet to the growing amino acid chain. Viruses that infect cells carry their own genetic material and occasionally, they make messenger RNAs that contain a specific signal (called a frameshift signal) that tells the ribosome to stop making one type of triplet and to start making another. The result is that one messenger RNA can make two proteins. This is typical of viruses; as their own genetic material is usually relatively small, they use all sorts of tricks to maximise the number of proteins they can make. In this project, we wish to examine what happens to the ribosome when it encounters a frameshift signal. The question is 'what happens to the ribosome that makes it misbehave?' To answer this, we will purify ribosomes caught in the act of translating through the frameshift signal and study them by microscopy. The microscopy technique we will use is based on electrons rather than light, so is extremely powerful, and is called cryo-electron microscopy. It is 'cryo' because the samples are frozen in aqueous solution before examination to keep them in a natural and stable state. The images we obtain will hopefully tell us something about how the frameshift signal interferes with the ribosome, and should also be informative about how ribosomes work during normal protein synthesis.