The rescue of stalled translation complexes: recoding of a sense to a nonsense codon

核糖体通过读取或“翻译”信使RNA （mRNA）中的信息来合成细胞中的所有蛋白质，而信使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一定的规则，即遗传密码，在遗传密码中，每个核苷酸三联体总是以同样的方式被读取，以启动、继续或终止一个完整蛋白质的合成。翻译的保真度极高，很少出错。然而，令人惊讶的是，有时核糖体会被提示忽略这个密码，通常是由正在读取的mRNA中的特定序列或刚刚由核糖体合成并仍在其中的蛋白质序列引起的。这种“重新编码”事件经常在病毒rna中发现，并允许病毒从非常紧凑、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mrna上，对蛋白质的正确表达非常重要。在许多情况下，重新编码事件允许正常的“停止”信号被绕过，这意味着蛋白质的结束，导致蛋白质的延伸。我们发现了一个新的重编码事件，核糖体被提示停止翻译，然后在没有正常信号的情况下重新启动，从而从一个mRNA中生成两个独立的蛋白质。这是由病毒的短肽序列“2A”决定的，它提供了一个重要而方便的工具，可以在不需要多个mrna的情况下共表达多个蛋白质，也有可能深入了解核糖体的工作原理。了解这一事件可能有另一个重要的影响，因为它可能有助于开发抗病毒策略，旨在抑制病毒感染期间的这一重新编码事件。因此，我们的目标是详细了解由2A决定的反应，确定所需的所有因素以及它所影响的细胞功能。到目前为止，我们已经发现2A肽导致核糖体暂停，并且通常催化在停止信号处终止翻译的“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暂停在2A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.