mRNA selection for translation: beyond the canonical view

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A central tenet of biology is that information found in the DNA of genes is converted into a messenger RNA molecule (mRNA), which is then translated into a chain of amino acids called a 'protein'. Proteins carry out most biological functions, catalyzing metabolic reactions as well as serving structural and regulatory roles. The complement of mature proteins present in a cell dictate its identity, function and health. Therefore, it is critical to all life that cells have the capacity to control which proteins are produced, when they are produced, their level when produced and their site of production within the cell. Some of the most abundant proteins in the cell such as proteins involved in the production of energy and in the production of proteins themself are often 1000s of times more abundant than other more regulatory proteins. One key stage where these controls are evident is when the machine for producing proteins, termed the ribosome, is recruited to the RNA. Scientists over the last 50 years have gradually pieced together a pathway involving a series of protein factors that are important in the translation of mRNA. More recently they have added the precise structures of the individual molecules within many of these proteins. Overall, this has led to a canonical textbook model for the process of ribosome recruitment to an mRNA that is conserved from yeast to human cells and is called the translation initiation pathway.In our recent work, we have used the relatively simple yeast model system to ask- how well do the 1000s of different mRNA molecules present even in a simpler cell interact with these different translation factors? This work has led to a surprising observation. Many of the mRNAs producing the most abundant proteins in the cell - proteins critical for fundamental pathways of life - interact poorly with these translation factors. This then begs a question- how do these mRNAs that are fundamental to all living systems effectively compete for ribosomes in a sea of other mRNAs? Hence, we started to look at where mRNAs are translated within cells. Again, we were surprised to find that many of the fundamental mRNAs described above are translated at specific sites that have been termed 'translation factories'. It makes sense to produce these proteins in a special place within the cell, as it means the process can be fine-tuned and co-ordinated without interfering with more general production of proteins. However, the rules that decide which mRNAs are translated in a local factory and the protein factors involved in the translation process in these sites are very poorly understood. Therefore, in this proposal, we will determine the molecular rules that enable translation of fundamental heavily translated mRNAs. This will include the RNA sequences and protein factors involved in translation factories, the role of canonical translation factors at these sites, and the importance of these mechanisms for a cell's life. A greater understanding of how cells prioritise the mRNAs that are translated into protein will have immediate applications in the production of medical and commercial proteins - enabling high level expression of valuable proteins, and will also impact upon studies of disease- from diseases where proteins aggregate in cells such as Parkinson's to nutritional diseases associated with deficiencies in particular proteins involved in metabolism.