TSC (Temperature Sensitive suppressors of the Calcium sensitivity of csg2 delta) Mutants; A Tool to Investigate Sphingolipid Metabolism in the Yeast Saccharomyces cerevisiae
UNIFORMED SERVICES UNIV OF THE HEALTH SCIENCES BETHESDA MD BETHESDA United States
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Sphingolipids are essential components of eucaryotic cell membranes but the basis of this essential nature is not understood. Sphingolipids and their metabolites have been implicated in a wide range of critical cell functions ranging from regulating cellular processes to fulfilling a membrane structural role. Defects in sphingolipid metabolism are a known cause of many diseases. To gain a more clear understanding of sphingolipid homeostasis, a genetic approach to their study was undertaken in the yeast Saccharomyces cerevisiae using the csg2A mutant. The csg2A mutant fails to mannosylate sphingolipids and exhibits a Ca2 sensitive phenotype not seen in wild type cells. Suppressors to the Ca2 sensitivity of csg2A possess mutations in genes prior to of the mannosylation step of sphingolipid biosynthesis resulting in decreased synthesis or altered structure of the toxic, unmannosylated intermediate lPC-e. Identification of these suppressor genes may help elucidate the reactions occurring in sphingolipid synthesis. A collection of csg2A suppressor mutants was made which possess a secondary ts conditional lethal phenotype to facilitate cloning by complementation. This collection is referred to as the tsc collection or Temperature Sensitive suppressors of the Calcium sensitivity of csg2A. Fifty-nine ts suppressors were isolated which possess mutations in one of IS genes tscl-tscl5. Of the 15 genes responsible for the tsc mutations, 11 have been identified. TSCI and TSC2 encode subunits of the serine palmitoyl transferase SPT and were previously identified as LCB2SCSl and LCBl respectively. TSC3 encodes a previously uncharacterized 80 amino acid protein involved in SPT activity. TSC4 and TSC5 are allelic to FAS2 which encodes the alpha-subunit of fatty acid synthase responsible for the synthesis of palmitoyl CoA in the cell. TSC6 encodes the very long chain fatty acid hydroxylase previously identified as SCS7. TSC7 is allelic to SUR2.