Yeast Genetics and Molecular Biology 2000
University of Washington
Seattle, Washington USA
July 2000

Name: Kohlwein, Sepp D.
Mailing Address: Department of Biochemistry, Technical University Graz, Petersgasse 12, Graz, A8010, Austria
Email Address: kohlwein@ftugax.tu-graz.ac.at
Phone & FAX numbers: 01143 316 873 6456 & ++873 6952

#041

The TSC13/YDL015c Gene Product is Required for Fatty Acid Elongation and is Localized to a Novel Structure at the Vacuolar/Nuclear Interface.
Sepp D. Kohlwein (1), Sandra Eder (1), J.Y. Choi (2), Charles E. Martin (2), Ken Gable (3), Dagmar Bacikova (3), Teresa Dunn (3)
(1) Department of Biochemistry, Technical University Graz, Petersgasse 12, Graz, A8010, Austria; (2) Rutgers University Biological Sciences Busch Campus PO Box 1059 Piscataway, NJ 08855-1059; (3) Uniformed Serv University Hlth Sci Department Biochemistry 4301 Jones Bridge Rd Bethesda, MD 20814-4799

The essential TSC13/YDL015c gene was identified in a screen for temperature sensitive suppressors of the Ca2+ sensitivity of csg2-delta mutants. Several of the TSC gene products are involved in sphingolipid synthesis. In yeast, the fatty acid moiety of ceramides and sphingolipids is a C26 very long-chain fatty acid (VLCFA) that is synthesized by a microsomal enzyme system that lengthens palmitate produced by cytosolic fatty acid synthase (FAS). Each cycle of elongation extends the fatty acid by 2 carbon units in a series of four enzymatic steps, using malonyl-CoA analogous to the FAS reaction. Biochemical evidence suggests that the TSC13 gene product is the enoyl reductase enzyme that catalyzes the last step in each cycle of elongation. The phenotypes of a tsc13 mutant - temperature sensitivity, accumulation of long chain bases and decreased VLCFA levels - are exacerbated by deletion of either ELO2 or ELO3, or by compromising the activity of the malonyl-CoA-providing enzyme, acetyl-CoA carboxylase, all of which have previously been shown to reduce VLCFA synthesis. Furthermore, Tsc13p co-immunoprecipitates with Elo2p and Elo3p, suggesting that the elongating proteins may be organized in a complex. A Tsc13p-GFP fusion revealed a unique staining pattern at the interface between the nucleus and vacuole. The role of this junction in the context of de novo fatty acid synthesis and elongation, ER-vacuole interaction, and exit from the ER in the secretory pathway will be discussed.

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