While natural products have long been a valuable source of biologically active compounds, their cellular targets and modes of action are rarely identified. In this project, yeast surface display (YSD) was investigated as a platform technology to rapidly identify the cellular targets of natural products. YSD involves cloning a cDNA library into baker's yeast (Saccharomyces cerevisiae) such that the encoded foreign proteins are expressed fused to the yeast Aga2 surface receptor. Flow cytometry

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... CS) is then used to separate yeast cells displaying proteins capable of binding to a fluorescently tagged probe, thereby allowing the cellular targets of the probe to be identified. In Part 1 of this project, a YSD clone displaying the well-studied human protein FKBP was constructed as a positive control. A fluorescently labelled analogue of FK506 (a known inhibitor of FKBP) was then used to optimise a range of FACS parameters for protein-small molecule interactions, including probe concentration, incubation time/temperature, detergent concentration, washing stringency and FACS binning stringency. In Part 2, a YSD cDNA library was constructed from the model nematode Caenorhabditis elegans. These preliminary studies have laid the groundwork for future YSDstudies to identify the cellular targets of a range of biologically active natural products.