We study the mechanism and regulation of protein synthesis in eukaryotic cells. Protein synthesis is part of the process of gene expression whereby cells decode the genetic information held within the genome and convert these molecular instructions into proteins. Cells only make the proteins they need when they are required. Organisms also have to adapt to changing environments and stresses (temperature, sunlight, infection etc) and adapting the set of proteins made by cells contributes to the adaptability of life. We use baker’s yeast (Saccharomyces cerevisiae) as a simple cellular model organism to study the molecular mechanisms controlling how cells regulate the sets of proteins that they require. Because of evolutionary conservation of mechanisms, insights gained from our studies are relevant to human cells and human diseases. We are able to create simple cell models that mimic aspects of human disorders.
Protein synthesis is the process of decoding an mRNA sequence into a functional protein. This is central to all cellular activity and is a major energy consumer within all cells. In eukaryotes, protein synthesis or 'translation' is mediated via a highly-conserved set of protein factors which interact with each mRNA and the ribosome. Translation is highly dynamic and must be flexible to change which proteins are made in response to a large number of input signals. Therefore gene expression controls at the level of translation are critical to a large number of normal cellular processes. For example they are important for stress responses, normal development of embryos and for memory formation in the brain.
The Pavitt lab studies aspects of translation and its control using a range of biochemical and genetic approaches. We primarily make use of the yeast Saccharomyces cerevisiae as a model organism with well developed genetic and biochemical tools to study fundemental biochemical processes. The protein synthesis factors we study as well as many of the key regulatory mechanisms are conserved from yeast to man, making findings in yeast directly relevant to human translation. For example we have used yeast to model effects of mutations in translation factors responsible for human diseases.
Translational Control of eIF2 by eIF2B and eIF5. The molecular mechanism of gene regulation in response to stress is being investigated. A regulatory mechanism, common to all eukaryotic cells, and termed the integrated stress response involves translational control by phosphorylation of translation factor eIF2, a GTP and initiator tRNA binding protein. One key step at the core of the control pathway is the inhibition of the translation factor eIF2B, a guanine nucleotide exchange factor (GEF) (red arrows in the figure). One aim of our work is to understand how eIF2B functions and we have developed a range of biochemical assays to study this. We have identified novel regulatory mechanisms and steps in protein synthesis initiation. For example, we identified that eIF5, has a novel GDP-dissociation inibitor (GDI) activity which antagonises the function of eIF2B and is critical for the response to phosphorylated eIF2. In addition we have found that eIF2B can actively displace eIF5 from eIF2 (GDF function) so that eIF2B can then perform its nucleotide exchange function. We have now shown that eIF2B can also antagonise eIF2 when bound to GTP and tRNA, this we call 'fail-safe control'. In colaboration with the Roseman lab, we have also determined the eIF2/eIF2B co-structure by cryoEM.