Polarized protein secretion is an essential process for the delivery of various proteins and lipids in eukaryotic cells to their correct locations. Our research focuses on the Sec6 protein, a component of an eight-subunit complex named exocyst, which is required for the direct delivery of cargos to the plasma membrane. An earlier study published on Sec6 (Sanger and Munson 2009) explored new Sec6 mutant proteins with altered the amino acids located on the surface of the protein. It was established that these mutations resulted in a temperature sensitive growth defect at 37 °C. However, despite the poor growth of these cells, the assembly of all 8 exocyst components was not affected, yet the complex appears to be missing from the site where they are expected to localize. Our current hypothesis is that Sec6 has an important anchoring function for the exocyst, and that the mislocalization of the exocyst stems from disruption of Sec6’s surface interaction with an unknown factor(s) on the plasma membrane. To identify the potential anchoring factors, we employed a yeast genetic screen using a multicopy plasmid based genomic library. The genetic screen employed the transformation of the library plasmid into sec6-49 via electroporation followed by growth assays to identify transformants overcoming the growth defect at 37°C. These surviving yeast colonies were subjected to plasmid extraction and DNA sequencing to identify the genomic segment on the plasmid. We successfully isolated 23 plasmids and sequenced several of them to identify open reading frames of the genes potentially responsible for the rescue of growth defect. Currently, we have narrowed it down to 5 specific candidate genes, LSB5, SRO9, STE50, BIK1, FUS1, and are testing the rescue effect of each individual gene. The isolation and characterization of novel anchoring interactors will shed light on mechanistic details of Sec6’s function in exocytosis.

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