Feedback control of translation termination in yeast

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At the cellular level, all life is dependent upon using the genetic information stored in DNA to make proteins. These proteins, through their action as catalysts, conduct the biochemical reactions in the cell. In order to make proteins, genetic information at the DNA level is first copied into a second, chain-like molecule, called mRNA. Finally, the genetic information now encoded within the mRNA is then read, or 'translated', into protein by a complex biochemical assembly called a ribosome. The process of translation is itself extremely complex, but essentially can be divided into three phases; initiation, where the ribosome joins the mRNA to start translation; elongation, where the mRNA genetic information is read to make the protein; and termination, when the ribosome leaves the mRNA. It is this last stage that forms the focus of this research. It is crucial that translation is terminated efficiently. If the ribosome stops too early, an incomplete protein is made, which will be non-functional. Crucially, such 'premature' stop events can be caused by mutations, such as some of the DNA defects underlying diseases like cystic fibrosis. In many cystic fibrosis patients, the DNA mutation in the cystic fibrosis gene, when copied into mRNA and translated by the ribosome, causes a short, non-functional protein to be made. The absence of the full-length product produces the symptoms of the disease. Understanding the way in which DNA mutations direct the manufacture of truncated proteins requires a fundamental knowledge of the termination stage of translation, and of the way that the ribosome responds to mutations in the genetic information. The complexity of process demands that new tools are developed to investigate the biochemistry that underpins the process. One such set of tools, mathematical and computational modelling, can be used to generate a quantitative description of translation and the termination step. Once modelled, translation can be studied using computer simulations, in parallel with laboratory experimental investigations. Modelling of biochemical processes is an emerging field that offers exciting prospects for understanding the complexity of cellular control circuits. In this proposal, biologists will work collaboratively with control/system engineers to model the translation process, including the termination step. The termination process of the model organism baker's yeast will be studied, due to the similarity of the process in yeast and human cells. In addition, there exist a series of yeast mutants that highlight feedback control of the translation termination step. Study of these mutants, and of how the feedback loop is controlled, provides an exciting opportunity to investigate many of the parameters that control protein synthesis and that regulate the length of all proteins in the cell. This understanding can, in the longer term, be applied to the study of the effects of human genetic diseases like cystic fibrosis.