Phosphatidylcholine and N-Methylated Phospholipids Are Nonessential in Saccharomyces cerevisiae

Phosphatidylcholine (PtdCho) is the most abundant phospholipid in numerous eukaryotes and is generally thought to be essential for membrane structure and cellular function. We designed a specific test of this idea by using genetic and biochemical manipulation of yeast. Yeast mutants (pem1 pem2Δ) lacking the phosphatidylethanolamine (PtdEtn) methyltransferase enzymes require choline for growth and cannot make N-methylated phospholipids. When these strains are grown on a glucose carbon source supplemented with 20 mm propanolamine (Prn), the PtdCho level declines precipitously to the limits of detection (<0.6%), and the hexagonal phase-forming, primary amine-containing lipids, PtdEtn and PtdPrn, constitute ∼60% of the total phospholipid content of the cell. When the lipids were analyzed by mass spectrometry, there was no compensatory shift in unsaturation of the PtdEtn and PtdPrn toward more bilayer-forming species. Thus the majority of the cellular amino phospholipids remained hexagonal phase-forming. The pem1 pem2Δ cells will also grow without choline, in the presence of Prn, on nonfermentable carbon sources (requiring functional mitochondria) and accumulate nearly 70% of their phospholipid as hexagonal phase-forming types. These data provide compelling evidence that the functions of PtdCho and N-methylated lipids in membranes are nonessential in Saccharomyces cerevisiae. Phosphatidylcholine (PtdCho) is the most abundant phospholipid in numerous eukaryotes and is generally thought to be essential for membrane structure and cellular function. We designed a specific test of this idea by using genetic and biochemical manipulation of yeast. Yeast mutants (pem1 pem2Δ) lacking the phosphatidylethanolamine (PtdEtn) methyltransferase enzymes require choline for growth and cannot make N-methylated phospholipids. When these strains are grown on a glucose carbon source supplemented with 20 mm propanolamine (Prn), the PtdCho level declines precipitously to the limits of detection (<0.6%), and the hexagonal phase-forming, primary amine-containing lipids, PtdEtn and PtdPrn, constitute ∼60% of the total phospholipid content of the cell. When the lipids were analyzed by mass spectrometry, there was no compensatory shift in unsaturation of the PtdEtn and PtdPrn toward more bilayer-forming species. Thus the majority of the cellular amino phospholipids remained hexagonal phase-forming. The pem1 pem2Δ cells will also grow without choline, in the presence of Prn, on nonfermentable carbon sources (requiring functional mitochondria) and accumulate nearly 70% of their phospholipid as hexagonal phase-forming types. These data provide compelling evidence that the functions of PtdCho and N-methylated lipids in membranes are nonessential in Saccharomyces cerevisiae. Phosphatidylcholine (PtdCho) 1The abbreviations used are: PtdCho, phosphatidylcholine; PtdEtn, phosphatidylethanolamine; Etn, ethanolamine; Cho, choline; Prn, propanolamine; Etn(Me), monomethylethanolamine; Etn(Me)2, dimethylethanolamine; PtdPrn, phosphatidylpropanolamine; PtdIns, phosphatidylinositol; PtdEtn(Me), phosphatidylmonomethylethanolamine; PtdEtn(Me)2, phosphatidyldimethylethanolamine; PSD, phosphatidylserine decarboxylase. is the most abundant phospholipid in many eukaryotic cells and has generally been assumed to be essential for cell viability (1Howe A.G. McMaster C.R. Biochim. Biophys. Acta. 2001; 1534: 65-77Crossref PubMed Scopus (27) Google Scholar, 2Vance J.E. Vance D.E. Biochem. Cell Biol. 2004; 82: 113-128Crossref PubMed Scopus (267) Google Scholar, 3Schneiter R. Brugger B. Sandhoff R. Zellnig G. Leber A. Lampl M. Athenstaedt K. Hrastnik C. Eder S. Daum G. Paltauf F. Wieland F.T. Kohlwein S.D. J. Cell Biol. 1999; 146: 741-754Crossref PubMed Scopus (381) Google Scholar). In this study we designed experiments to test whether PtdCho or its N-methylated lipid precursors were truly essential for the yeast Saccharomyces cerevisiae. In S. cerevisiae, PtdCho can be synthesized by the pathway PtdSer → PtdEtn → PtdEtn(Me) → PtdEtn(Me)2 → PtdCho as outlined in Fig. 1. Pem1p and Pem2p are methyltransferases that synthesize PtdCho from PtdEtn (4Summers E.F. Letts V.A. McGraw P. Henry S.A. Genetics. 1988; 120: 909-922Crossref PubMed Google Scholar, 5Kodaki T. Yamashita S. J. Biol. Chem. 1987; 262: 15428-15435Abstract Full Text PDF PubMed Google Scholar). When ethanolamine (Etn) and choline (Cho) are present, PtdEtn and PtdCho are synthesized via the Kennedy pathways that use CDP-ethanolamine and CDP-choline intermediates. PtdEtn derived from the Kennedy pathway can also be methylated to form PtdCho (6Carman G.M. Henry S.A. Prog. Lipid. Res. 1999; 38: 361-399Crossref PubMed Scopus (263) Google Scholar). Phosphoethanolamine, an intermediate in the Kennedy pathway, can also be synthesized as a consequence of sphingolipid degradation (7Saba J.D. Nara F. Bielawska A. Garrett S. Hannun Y.A. J. Biol. Chem. 1997; 272: 26087-26090Abstract Full Text Full Text PDF PubMed Scopus (213) Google Scholar, 8Storey M.K. Clay K.L. Kutateladze T. Murphy R.C. Overduin M. Voelker D.J. J. Biol. Chem. 2001; 276: 48539-48548Abstract Full Text Full Text PDF PubMed Scopus (101) Google Scholar). Monomethylethanolamine (Etn(Me)) and dimethylethanolamine (Etn(Me)2) can also be assimilated into PtdEtn(Me) and PtdEtn(Me)2, respectively, via the Kennedy pathways. Yeast mutants (pem1 pem2Δ) lacking the methyltransferase enzymes cannot make N-methylated phospholipids by the de novo pathway. The growth defect of these mutants can be rescued by choline, Etn(Me)2, or Etn(Me) but not by Etn (4Summers E.F. Letts V.A. McGraw P. Henry S.A. Genetics. 1988; 120: 909-922Crossref PubMed Google Scholar). These findings have led to the conclusions that some form of methylated PtdEtn is essential for yeast growth (1Howe A.G. McMaster C.R. Biochim. Biophys. Acta. 2001; 1534: 65-77Crossref PubMed Scopus (27) Google Scholar, 4Summers E.F. Letts V.A. McGraw P. Henry S.A. Genetics. 1988; 120: 909-922Crossref PubMed Google Scholar). To test if PtdCho and N-methylated lipids are critical for cell viability, we examined whether propanolamine (Prn), an ethanolamine analogue, could rescue the growth defect of methylation-defective mutant strains. Previous research showed that yeast mutants (psd1Δ psd2Δ) lacking PtdSer decarboxylases require Cho or Etn for growth but can also grow on Prn (8Storey M.K. Clay K.L. Kutateladze T. Murphy R.C. Overduin M. Voelker D.J. J. Biol. Chem. 2001; 276: 48539-48548Abstract Full Text Full Text PDF PubMed Scopus (101) Google Scholar). Mutant strains supplemented with Prn accumulate a novel lipid, phosphatidylpropanolamine (PtdPrn). PtdPrn can comprise up to 40% of the total phospholipid content in Prn-supplemented cells, at the expense of PtdCho and PtdEtn. In Prn-supplemented cells with psd1Δ psd2Δ mutations, the PtdCho content was reduced from 38 to 10% total phospholipid, and the PtdEtn content was reduced to 1% of total phospholipid. This result suggests that with appropriate genetic manipulation PtdPrn might be able to replace the entire PtdCho and PtdEtn pools. Under physiological conditions, unsaturated PtdCho, PtdSer, and PtdIns all form bilayers when hydrated, but PtdEtn and PtdPrn form a hexagonal phase in vitro (8Storey M.K. Clay K.L. Kutateladze T. Murphy R.C. Overduin M. Voelker D.J. J. Biol. Chem. 2001; 276: 48539-48548Abstract Full Text Full Text PDF PubMed Scopus (101) Google Scholar, 9Cullis P.R. de Kruijff B. Biochim. Biophys. 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In this study we applied genetic and biochemical approaches to determine whether: 1) PtdCho and its N-methylated phospholipid precursors could be eliminated from cells without loss of viability; 2) PtdCho could also be eliminated for growth on both a fermentable carbon source (glucose) and a nonfermentable carbon source (requiring functional mitochondria); and 3) PtdCho depletion was accompanied by a shift to more saturated species of primary amine-containing phospholipids. The results demonstrate that PtdCho and N-methylated phospholipids are nonessential in yeast and are not required for mitochondrial function. Construction of Methylation-defective Strains—Deletion mutants for the PEM2 gene were generated by homologous recombination in the RYY52 strain (Matα, trp1, lys2, ura3, leu2, his3, suc2, psd1Δ-1::TRP1) (14Wu W.I. Routt S. Bankaitis V.A. Voelker D.R. J. Biol. Chem. 2000; 275: 14446-14456Abstract Full Text Full Text PDF PubMed Scopus (68) Google Scholar) by transformation with PCR products harboring a KanMX sequence. These PCR products were made by using primers identical to a 24-nucleotide sequence, 541 bp upstream of PEM2, and a 22-nucleotide sequence, 545 bp downstream of PEM2. Chromosomal DNA templates for the PCR were prepared from a pem2Δ strain (Research Genetics, Inc.) in which the entire PEM2 coding sequence was deleted and replaced by KanMX. The resulting psd1Δ pem2Δ strain was isolated by selection for G418 resistance. Correct replacement of PEM2 by the KanMX sequence was confirmed by PCR analysis using primers outside of the target sequence and a primer specific to the KanMX sequence. Disruption of the PEM1 gene was accomplished by homologous recombination of the psd1Δ pem2Δ strain using transformation with PCR products containing a 3.2-kb pem1::LEU2 cassette. The pem1::LEU2 module was amplified by PCR from the pem1 disruption strain ESXI-1(4d) obtained from Dr. Susan Henry (Cornell University). The disruption of the PEM1 gene was verified by PCR using one primer within LEU2 and the other outside of the target locus. Strains with a functional Psd1p were generated from pem1 pem2Δ psd1 mutant strains by transformation with a YCp50-PSD1 plasmid. Growth Measurement of Lipid Methylation-defective Strains—The methylation-defective strains (pem1::LEU2 pem2Δ::KanMX or pem1::LEU2 pem2Δ::KanMX psd1Δ::TRP1) were pre-grown at 30 °C on synthetic complete medium plates containing Prn (20 mm) to dilute out cellular PtdCho. The cells were next inoculated into synthetic complete lactate or glucose medium and washed twice with the same medium. Cells were re-inoculated at an A600 of 0.005 in synthetic glucose or 0.02 in synthetic lactate medium plus or minus 20 mm Etn, 20 mm Prn, or 2 mm Cho. Cell growth at 30 °C was monitored by culture absorbance at 600 nm. Lipid Phosphorus Measurement—Lipid methylation-defective strains were grown to mid-log phase at 30 °C in synthetic glucose or semi-synthetic lactate (2% lactate and 0.05% glucose) media plus Prn (20 mm) or Cho The cells were by and washed twice with were prepared as PubMed Scopus Google Scholar). The lipids were from cells and as Voelker D.R. J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google Scholar). The phospholipids were by on plates using by were with and by G. S. PubMed Scopus Google Scholar). The results are as the of total lipid in phospholipid are S.D. for or from the cells grown in synthetic complete medium with glucose plus Prn (20 mm) or Cho mm) were by as Lipid to PtdPrn, PtdEtn, or PtdCho were into and from the by the of and J. Biochem. PubMed Scopus Google Scholar). in were analyzed with a mass to experiments a and by using mass was in the with a to the detection of all for an for species of PtdCho M. Murphy R.C. Rev. PubMed Scopus Google Scholar). The next the mass to the loss of a loss of the PtdEtn species Murphy R.C. Chem. PubMed Scopus Google Scholar). The next the loss of of PtdPrn as the homologous to the loss of for PtdEtn. The next a mass of from The was in the the mass from In experiments phospholipid were by from the and examined by in the were analyzed in the of the for of or in to determine the in using C. K. S. Murphy R.C. Chem. Res. PubMed Scopus Google Scholar). We also experiments to out the that the Prn used in these was by Cho. The Prn was analyzed by mass that was for both the presence of Prn as as Cho was no evidence for the of Cho in the Prn at a level as by a of at when the for was of choline analyzed the propanolamine generated a as for this Prn of Methylation-defective Growth on and strains that have in PEM1 and PEM2 cannot make PtdCho and N-methylated lipids (4Summers E.F. Letts V.A. McGraw P. Henry S.A. Genetics. 1988; 120: 909-922Crossref PubMed Google Scholar). These mutant cells were grown in the presence of Prn to to make PtdPrn via the Kennedy pathway as in Fig. The mutant strains on glucose media supplemented with when lipids from these were by and with there was a in the PtdCho This was as PtdCho by mass of this PtdCho that of total phospholipids not with findings (8Storey M.K. Clay K.L. Kutateladze T. Murphy R.C. Overduin M. Voelker D.J. J. Biol. Chem. 2001; 276: 48539-48548Abstract Full Text Full Text PDF PubMed Scopus (101) Google this result of PtdCho can without cell These data also that of choline can be derived from was to all PtdCho and N-methylated precursors from these yeast all growth were in In yeast mutants (pem1 pem2Δ) lacking the methyltransferase enzymes cannot make N-methylated phospholipids. The growth defect of the mutants can be rescued by choline, Etn(Me)2, or Etn(Me) but not by To whether PtdCho and N-methylated lipids are critical for cell viability, we the growth of the lipid methylation-defective mutant strain on glucose media supplemented with Etn, Prn, Cho, or no phospholipid or Etn to growth of the mutant the strain when with Cho. In the presence of Prn the with a but nearly the same level obtained with Cho from the cells grown on Cho or Prn medium were by In the presence of Cho, PtdCho was as the phospholipid. In the of Cho but the presence of Prn, the lipid of the lipid methylation-defective mutant showed The PtdCho and a novel lipid, PtdPrn, was of lipid from the plates also confirmed the PtdCho was reduced to the limits of The PtdIns more and PtdPrn for of the total phospholipid. with Prn the hexagonal phase lipids PtdEtn and PtdPrn of the total phospholipid. in the of in PtdEtn and of total hexagonal phase lipids and in the mutants supplemented with Prn might result in to make a compensatory shift in the of of these lipids toward more bilayer-forming species. To test this idea the species of PtdEtn, PtdPrn, and PtdCho were analyzed by mass of species was in yeast grown in the presence of choline, species of PtdEtn were at and The of these species was of of these which the to of generated one at of the at both and of this PtdEtn species of a of the species to but a abundant species at the same mass to was also in the at analysis of and the species and with of of the with the species isolated from the yeast was by the a of species with as the more abundant species was to to the species in the PtdEtn When cells were with there was no in the species within the phosphatidylethanolamine species at the level of or their products PtdPrn species were at and which to and plus The of these were confirmed by mass This of the species and that the saturated species were not in the PtdPrn and PtdEtn of the mutant supplemented with analysis that there is no shift in the of in PtdEtn and PtdPrn when the PtdCho is Lipid of pem1 pem2Δ mutant strains were by and the to PtdPrn, PtdEtn, or PtdCho were from the and in to mass mass of PtdEtn of mutant cells supplemented with the of species. The of the species was by of the in the that the as a species of PtdCho in cells with the the of the species of PtdEtn from cells with the the of the species of PtdPrn from cells with the the of the Prn Growth of Methylation-defective and the PtdCho Under are required when yeast cells grow on carbon sources and use for We analyzed cell growth to determine whether PtdPrn could mitochondrial function. this the methylation-defective mutants were grown on lactate media without or with Etn, Prn, or Cho and with Etn to the growth of methylation-defective strains. In the mutants when with Cho. In a the mutants also when supplemented with from the cells grown on lactate medium supplemented with Cho or Prn were by with glucose grown cells, the mutants grown in lactate medium supplemented with Prn showed in lipid of phospholipids on by that PtdCho to the limits of The loss of PtdCho was accompanied by a in PtdIns and the of PtdPrn as of the total phospholipid. Under these the hexagonal phase lipids PtdEtn and PtdPrn for more of the phospholipid We also examined the of the methyltransferase and Prn the lipid of isolated The results of this analysis are in Fig. and demonstrate that the mitochondrial phospholipid that for the cell. The findings demonstrate that PtdCho is not essential for mitochondrial and that the can a hexagonal phase lipid content of of its total phospholipid. Cells PtdCho and the to PtdEtn with Prn on research (8Storey M.K. Clay K.L. Kutateladze T. Murphy R.C. Overduin M. Voelker D.J. J. Biol. Chem. 2001; 276: 48539-48548Abstract Full Text Full Text PDF PubMed Scopus (101) Google Scholar, R. M. R. Daum G. Biol. 2001; PubMed Scopus Google Scholar) has that mitochondrial PtdEtn generated by Psd1p is critical for the growth of yeast strains. We experiments to test if mitochondrial PtdEtn as as PtdCho can be replaced by PtdPrn We used mutant strains in PEM1 and PEM2 for phospholipid and in for PtdEtn in The in the gene results in a in the PtdEtn in The mutants were grown on glucose media lacking or with Etn, Prn, or Cho of the mutant without or with Etn to In the strain when with Cho. The strain also with Prn a The results that Prn-supplemented mutants can grow genetic of PtdCho and mitochondrial PtdEtn lacking PtdCho and with reduced mitochondrial PtdEtn with Prn in glucose medium. The pem1 pem2Δ psd1 mutant strains were at 30 °C on synthetic lactate plates containing Prn (20 mm) to dilute out cellular PtdCho. Cells were inoculated into synthetic glucose medium and washed twice with the same medium. Cells were re-inoculated at an absorbance of 0.005 in synthetic glucose without or plus 20 mm Etn, 20 mm Prn, or 2 mm Cho. Cell growth at 30 °C was monitored by The data are from a one of from the cells grown on or media were by When the lipids were by the mutant strain grown on Prn PtdCho and PtdPrn In the PtdIns more in the mutant supplemented with Prn when with this strain supplemented with of the phospholipids the of PtdCho and a in PtdIns, and an of PtdPrn to of the total phospholipid cells, the Prn-supplemented cells not accumulate of We also isolated from cells harboring pem1 pem2Δ psd1Δ and the phospholipids of these The results in Fig. demonstrate that choline of the mutant in which PtdCho is the most abundant phospholipid and PtdIns, PtdEtn, and PtdSer are nearly from to of the total phospholipids. for a strain lacking the PtdEtn content of the is reduced by when with the level of this phospholipid in total cell membranes Fig. of the derived from the mutant supplemented with 2 mm Prn the are of PtdCho and PtdPrn as the most abundant phospholipid These also of PtdIns and of PtdEtn and PtdSer We next to determine whether PtdPrn could the growth of the mutant The results of these experiments are in Fig. Cells lacking both mitochondrial PtdCho and the of PtdEtn generated by Psd1p to grow with Prn functional These findings demonstrate that PtdPrn is to both PtdCho and PtdEtn for mitochondrial In experiments in this we the of PtdCho and other methylated of PtdEtn for the growth and mitochondrial of S. cerevisiae. In many eukaryotes used for biochemical PtdCho is the most abundant phospholipid and is assumed to be essential for membrane structure and and cell growth (1Howe A.G. McMaster C.R. Biochim. Biophys. Acta. 2001; 1534: 65-77Crossref PubMed Scopus (27) Google Scholar, 3Schneiter R. Brugger B. Sandhoff R. Zellnig G. Leber A. Lampl M. Athenstaedt K. Hrastnik C. Eder S. Daum G. Paltauf F. Wieland F.T. Kohlwein S.D. J. Cell Biol. 1999; 146: 741-754Crossref PubMed Scopus (381) Google Scholar, P.L. FASEB J. 1989; 3: 1833-1842Crossref PubMed Scopus (412) Google Scholar). The results of provide evidence that PtdCho, PtdEtn(Me), PtdEtn(Me)2 is required for cell viability or mitochondrial in yeast. to the of methylated of PtdEtn, PtdCho, in cell growth was to use the Etn Prn, Etn, a primary Previous have that Prn is into phospholipid in both Saccharomyces and species (8Storey M.K. Clay K.L. Kutateladze T. Murphy R.C. Overduin M. Voelker D.J. J. Biol. Chem. 2001; 276: 48539-48548Abstract Full Text Full Text PDF PubMed Scopus (101) Google Scholar, J.D. Biochem. J. 1988; PubMed Scopus Google Scholar). The of PtdPrn are to of PtdEtn. PtdPrn hexagonal phase that PtdPrn has a to form hexagonal phase structures PtdEtn (8Storey M.K. Clay K.L. Kutateladze T. Murphy R.C. Overduin M. Voelker D.J. J. Biol. Chem. 2001; 276: 48539-48548Abstract Full Text Full Text PDF PubMed Scopus (101) Google Scholar). PtdPrn hexagonal phase cannot for the cellular for PtdEtn in yeast. In in PtdPrn we that this novel lipid replaced of the PtdCho in cells and cells to with reduced of PtdEtn, by in PtdSer decarboxylases (8Storey M.K. Clay K.L. Kutateladze T. Murphy R.C. Overduin M. Voelker D.J. J. Biol. Chem. 2001; 276: 48539-48548Abstract Full Text Full Text PDF PubMed Scopus (101) Google Scholar). These led to the experiments in this study designed to test whether PtdPrn be for cell growth in the of PtdCho The experiments in and demonstrate that Prn strains harboring in PEM1 and PEM2 to at a the same cells supplemented with Cho. of the lipid of these cells cells grown on plates lacking choline, but supplemented with Prn, are able to synthesize of PtdCho. This result that of Cho that the cells are able to growth in no PtdCho was the of These data demonstrate that yeast not require PtdCho or the or of PtdEtn for Previous by (4Summers E.F. Letts V.A. McGraw P. Henry S.A. Genetics. 1988; 120: 909-922Crossref PubMed Google Scholar) that yeast cells could grow with PtdEtn(Me)2 PtdCho and with PtdEtn(Me) PtdCho but a specific for at some of PtdEtn as essential for in cells also evidence that PtdEtn(Me)2 could growth of cells containing of PtdCho J.D. M. S. A. PubMed Scopus Google Scholar). the complete replacement of PtdCho and all N-methylated of PtdEtn by the primary amine-containing and hexagonal phase-forming PtdPrn was We these to more growth by strains growth with cells grown on PtdPrn growth in the of PtdCho and other N-methylated phospholipids when functional were These results a of important mitochondrial and not require PtdCho or methylated PtdEtn. In the analysis of mitochondrial phospholipids in Fig. that PtdPrn is into this as as other We have data with choline and ethanolamine mutants that the of and in the of These findings are with choline J. Biol. Chem. 1987; 262: Full Text PDF PubMed Google Scholar) and J. Biol. Chem. 1988; Full Text PDF PubMed Google Scholar) as the in the of PtdPrn in the is that PtdPrn be synthesized in the and McMaster C.R. Biol. PubMed Scopus Google Scholar) and be to the the phospholipid that be to the of important from these experiments is that the functional with as as 70% of their of phospholipid containing primary (8Storey M.K. Clay K.L. Kutateladze T. Murphy R.C. Overduin M. Voelker D.J. J. Biol. Chem. 2001; 276: 48539-48548Abstract Full Text Full Text PDF PubMed Scopus (101) Google Scholar) that PtdPrn for of cellular PtdEtn we also whether PtdPrn could and replace the PtdEtn of Cells harboring the pem1 pem2Δ psd1Δ are to synthesize PtdCho by methyltransferase and mitochondrial PtdEtn by Psd1p In glucose medium these mutant strains grow with a but of when supplemented with PtdPrn replaced PtdCho, and the presence of the psd1Δ total cellular PtdEtn In psd1Δ strains grown without Etn, PtdEtn the of and to a the of and the of (7Saba J.D. Nara F. Bielawska A. Garrett S. Hannun Y.A. J. Biol. Chem. 1997; 272: 26087-26090Abstract Full Text Full Text PDF PubMed Scopus (213) Google Scholar, 8Storey M.K. Clay K.L. Kutateladze T. Murphy R.C. Overduin M. Voelker D.J. J. Biol. Chem. 2001; 276: 48539-48548Abstract Full Text Full Text PDF PubMed Scopus (101) Google Scholar). PtdEtn and content in the is also the by the mutant cells to lactate as the carbon source that functional for The growth in Fig. that the mutant cannot grow with Prn but can grow with Cho Thus PtdPrn can replace mitochondrial PtdCho when there is PtdEtn in the The PtdPrn to replace both PtdCho and PtdEtn within the These findings are with other that PtdEtn an essential in mitochondrial membrane structure and (8Storey M.K. Clay K.L. Kutateladze T. Murphy R.C. Overduin M. Voelker D.J. J. Biol. Chem. 2001; 276: 48539-48548Abstract Full Text Full Text PDF PubMed Scopus (101) Google Scholar, R. M. R. Daum G. Biol. 2001; PubMed Scopus Google Scholar). In all in this the of cells with Prn in of PtdIns when with cells supplemented with Cho. This was most when the phospholipids of the pem1 pem2Δ psd1Δ The of membrane PtdIns content the to replace some of the eliminated PtdCho with the PtdIns to the of PtdPrn and PtdEtn to form structures (8Storey M.K. Clay K.L. Kutateladze T. Murphy R.C. Overduin M. Voelker D.J. J. Biol. Chem. 2001; 276: 48539-48548Abstract Full Text Full Text PDF PubMed Scopus (101) Google Scholar). In this that is to the phospholipid of yeast and its with a of genetic and biochemical PtdCho, the lipid of many can be eliminated with other N-methylated of PtdEtn, that these phospholipids are The of PtdCho is both and growth