| Summary: | Maintaining the correct balance of the various proteins found within a cell is a major process. Many factors come together during gene expression to transcribe a gene into mRNA and translate this transcript into a polypeptide chain. These processes are themselves formed of many stages, each of which provides points for a cell to ensure accuracy and adjust the amount of a certain protein. At the end of translation, the eukaryotic release factors eRF1 and eRF3 interact to release the nascent polypeptide chain from the ribosome. The main question remaining to be answered is how release factor levels, and with them termination accuracy, are regulated in Saccharomyces cerevisiae. This study focused on transcription and translational, as well as post translational events, as possible points of regulation. Our findings suggest that there is no feedback mechanism at either transcription or translation level which allows a cell to sense and adjust cellular levels of either of the . release factors. Although both eRF1 and eRF3 were found to be highly stable under non- stress conditions, microscopy studies highlighted the possible involvement of the yeast vacuole in regulating translation factor abundance during environmental stress. While no significant level changes were observed for the class one release factor eRF1 and several elongation factors, eRF3 levels were found to increase in protease deletion strains. Levels of the release factor were furthermore affected by deletions of the N-terminus in part or as a whole, though no connection was found linking the N-terminal region of eRF3 and the vacuole to one another in regulating cellular levels of the release factor. Moreover, this study highlighted that release factor levels, their ratio to one another and other factors involved in translation, are inextricably linked to termination accuracy. Data produced by this investigation suggests that eRF3 levels and activity are affected by a network of other factors. In specific, data presented here support studies published by other Laboratories reporting a functional interaction between eRF3 and the nucleotide exchange factor eEF1B and suggest that eRF1 might act as TDI for eRF3, as seen in mammalian cells.
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