Molecular and Cellular Biology, January 2001, p. 109-125, Vol. 21, No. 1
0270-7306/01/$04.00+0 DOI: 10.1128/MCB.21.1.109-125.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.
SFB Biomembrane Research Center, Department of Biochemistry, Technical University Graz, A8010 Graz, Austria1; Division of Life Sciences, Bureau of Biological Research, Rutgers University, Piscataway, New Jersey 08854-80822; and Department of Biochemistry, Uniformed Services University of the Health Sciences, Bethesda, Maryland 208143
Received 8 August 2000/Returned for modification 13 September 2000/Accepted 3 October 2000
The TSC13/YDL015c gene was identified in a screen for
suppressors of the calcium sensitivity of csg2
mutants
that are defective in sphingolipid synthesis. The fatty acid moiety of
sphingolipids in Saccharomyces cerevisiae is a very long
chain fatty acid (VLCFA) that is synthesized by a microsomal enzyme
system that lengthens the palmitate produced by cytosolic fatty acid
synthase by two carbon units in each cycle of elongation. The
TSC13 gene encodes a protein required for elongation,
possibly the enoyl reductase that catalyzes the last step in each cycle
of elongation. The tsc13 mutant accumulates high levels of
long-chain bases as well as ceramides that harbor fatty acids with
chain lengths shorter than 26 carbons. These phenotypes are exacerbated
by the deletion of either the ELO2 or ELO3
gene, both of which have previously been shown to be required for VLCFA
synthesis. Compromising the synthesis of malonyl coenzyme A
(malonyl-CoA) by inactivating acetyl-CoA carboxylase in a
tsc13 mutant is lethal, further supporting a role of Tsc13p
in VLCFA synthesis. Tsc13p coimmunoprecipitates with Elo2p and Elo3p,
suggesting that the elongating proteins are organized in a complex.
Tsc13p localizes to the endoplasmic reticulum and is highly enriched in
a novel structure marking nuclear-vacuolar junctions.
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