The rescue of stalled translational conplexes: recoding of a sense to nonsense codon

核糖体通过读取或翻译信使RNA(信使RNA)中的信息来合成细胞中的所有蛋白质，信使RNA又是存储在细胞DNA中的信息的副本。核糖体的准确翻译依赖于它们遵守某些规则，即遗传密码，在这些规则中，每个核苷酸三联体总是以相同的方式被读取，以启动、继续或终止完整蛋白质的合成。翻译的保真度极高，几乎不会出错。然而，令人惊讶的是，有时核糖体会被提示忽略这一密码，通常是由于正在读取的信使核糖核酸中的特定序列或核糖体刚刚合成并仍在其内部的蛋白质序列。这样的“重新编码”事件经常在病毒RNA中发现，并使病毒能够从非常紧凑、高效的基因组中产生它们所需的所有蛋白质。一些重新编码事件也发生在细胞mRNAs上，对蛋白质的正确表达非常重要。在许多情况下，重新编码事件可以绕过表示蛋白质结束的正常“停止”信号，从而导致蛋白质的延伸。我们已经发现了一个新的重新编码事件，在这个事件中，核糖体被提示停止翻译，然后重新启动/没有正常的信号/从而从一个mRNA产生两个单独的蛋白质。这是由来自病毒的一段称为‘2A’的短肽序列决定的，它为多种蛋白质的共表达提供了一个重要而方便的工具，而不需要多个mRNAs，也为深入了解核糖体的工作原理提供了可能性。了解这一事件可能会有另一个重要的影响，因为它可能允许开发抗病毒策略，旨在抑制病毒感染期间的这种重新编码事件。因此，我们的目标是详细了解2A所决定的反应，确定所需的所有因素以及它影响的细胞功能。到目前为止，我们已经发现，2A肽导致核糖体暂停，而正常情况下催化在停止信号下终止翻译的‘释放因子’是发生在2A处的异常终止反应所必需的。我们将研究释放因子与在2A暂停的核糖体的相互作用，并试图确定是什么因素导致了暂停。

Ribosomes synthesise all the proteins in the cell by reading or 'translating' information in messenger RNA (mRNA), which in turn is a copy of information stored in the cell's DNA. Accurate translation by ribosomes relies on them obeying certain rules, the genetic code, in which each triplet of nucleotides is always read in the same way to initiate, continue or terminate synthesis of a completed protein. The fidelity of translation is extremely high, and very few errors are made. Surprisingly however, on occasion ribosomes are prompted to disregard this code, often by particular sequences in the mRNA that is being read or the protein sequence that has just been synthesized by the ribosome and is still inside it. Such 'recoding' events are often found in viral RNAs and allow viruses to generate all the proteins they need from very compact, efficient genomes. Some recoding events also take place on cellular mRNAs and can be very important for correct expression of proteins. In many cases recoding events allow the normal 'stop' signals that signify the end of a protein to be bypassed, leading to extension of the protein. We have uncovered a novel recoding event in which the ribosome is prompted to stop translation and then restart / without the normal signals for either / thereby generating 2 separate proteins from one mRNA. This is dictated by a short peptide sequences termed '2A' from viruses and provides both an important and convenient tool for co-expression of more than one protein without the need for multiple mRNAs, and also the possibility of insight into how the ribosome works. Understanding this event may have another important repercussions as it may allow development of antiviral strategies, aimed at inhibiting this recoding event during viral infection. Our aim is therefore to understand reaction dictated by 2A in detail, identify all the factors that are required and the cellular functions that it impinges on. Thus far we have found that the 2A peptide causes ribosomes to pause, and that the 'release factors' that normally catalyse termination of translation at a stop signal are required for the abnormal termination reaction that takes place at 2A. We will investigate the interactions of release factors with ribosomes paused at 2A and attempt to determine what factors contribute to the pause.