Elo1p-dependent carboxy-terminal elongation of C14 : 1 Delta(9) to C16 : 1Delta(11) fatty acids in Saccharomyces cerevisiae

Saccharomyces cerevisiae medium-chain acyl elongase (ELO1) mutants have pre viously been isolated in screens for fatty acid synthetase (FAS) mutants th at fail to grow on myristic acid (C14:0)-supplemented media. sere we report that wild-type cells cultivated in myristoleic acid (C14:1 Delta(9))-suppl emented media synthesized a novel unsaturated fatty acid that was identifie d as C16:1 Delta(11) fatty acid by gas chromatography-mass spectroscopy. Sy nthesis of C16:1 Delta(11) was dependent on a functional ELO1 gene, indicat ing that Elo1p catalyzes carboxy-terminal elongation of unsaturated fatty a cids (alpha-elongation), In wild-type cells, the C16:1 Delta(11) elongation product accounted for approximately 12% of the total fatty acids. This inc reased to 18% in cells that lacked a functional acyl chain desaturase (ole1 Delta mutants) and hence were fully dependent on uptake and elongation of C14:1. The observation that ole1 Delta mutant cells grew almost like wild t ype on medium supplemented with C14:1 indicated that uptake and elongation of unsaturated fatty acids were efficient. Interestingly, wildtype cells su pplemented with either C14:1 or C16:1 fatty acids displayed dramatic altera tions in their phospholipid composition, suggesting that the availability o f acyl chains is a dominant determinant of the phospholipid class compositi on of cellular membranes. In particular, the relative content of the two ma jor phospholipid classes, phosphatidylethanolamine and phosphatidylcholine, was strongly dependent on the chain length of the supplemented fatty acid. Moreover, analysis of the acyl chain composition of individual phospholipi d classes in cells supplemented with C14:1 revealed that the relative degre e of acyl chain saturation characteristic for each phospholipid class appea red to be conserved, despite the gross alteration in the cellular acyl chai n pool. Comparison of the distribution of fatty acids that were taken up an d elongated (C16:1 Delta(11)) to those that were endogenously synthesized b y fatty acid synthetase and then desaturated by Ole1p (C16:1 Delta(9)) in i ndividual phospholipid classes finally suggested the presence of two differ ent pools of diacylglycerol species. These results will be discussed in ter ms of biosynthesis of different phospholipid classes via either the de novo or the Kennedy pathway.