The Initial Step of the Glycerolipid Pathway

The initial step of phospholipid biosynthesis in yeast is carried out through the acylation of glycerol 3-phosphate (G-3-P) and dihydroxyacetone phosphate by stereospecific sn-1 acyltransferases. Here we report the identification of two key fatty acyltransferases of the glycerolipid biosynthesis pathway in Saccharomyces cerevisiae. Disruption of the open reading frame YBL011w, corresponding to a gene previously identified as a choline transporter suppressor (SCT1), resulted in a substantial decrease of total cellular G-3-P acyltransferase activity. A yeast strain disrupted at the open reading frame YKR067w, which encodes a protein closely related to Sct1p, also exhibited a dramatic reduction in G-3-P acyltransferase activity. Molecular characterizations of the genes revealed that a missense mutation in YKR067w accounted for a defect in the activities of the G-3-P acyltransferase in the yeast mutant strain TTA1. Heterologous expression of YKR067w in Escherichia coli further confirmed its enzyme activity. These results indicate that YKR067w and YBL011w, designated herein as GAT1 and GAT2(SCT1), respectively, are yeast G-3-P acyltransferase genes. Furthermore, biochemical results are presented to show that both Gat1p and Gat2p(Sct1p) are G-3-P/dihydroxyacetone phosphate dual substrate-specific sn-1 acyltransferases. The fatty acyl specificity of Gat1p is similar to that of the mammalian microsomal G-3-P acyltransferase, as it can effectively utilize a broad range of fatty acids as acyl donors. In contrast, Gat2p(Sct1p) displayed preference toward 16-carbon fatty acids. The most notable of the altered phospholipid compositions of the gat1Δ and g at2(sct1)Δ strains are a decreased phosphatidic acid pool and an increased phosphatidylserine/phosphatidylinositol ratio. This did not appear to affect the mutants as no growth defect was found. However, null mutations of both GAT1 and GAT2(SCT1) are synthetically lethal to yeast. The initial step of phospholipid biosynthesis in yeast is carried out through the acylation of glycerol 3-phosphate (G-3-P) and dihydroxyacetone phosphate by stereospecific sn-1 acyltransferases. Here we report the identification of two key fatty acyltransferases of the glycerolipid biosynthesis pathway in Saccharomyces cerevisiae. Disruption of the open reading frame YBL011w, corresponding to a gene previously identified as a choline transporter suppressor (SCT1), resulted in a substantial decrease of total cellular G-3-P acyltransferase activity. A yeast strain disrupted at the open reading frame YKR067w, which encodes a protein closely related to Sct1p, also exhibited a dramatic reduction in G-3-P acyltransferase activity. Molecular characterizations of the genes revealed that a missense mutation in YKR067w accounted for a defect in the activities of the G-3-P acyltransferase in the yeast mutant strain TTA1. Heterologous expression of YKR067w in Escherichia coli further confirmed its enzyme activity. These results indicate that YKR067w and YBL011w, designated herein as GAT1 and GAT2(SCT1), respectively, are yeast G-3-P acyltransferase genes. Furthermore, biochemical results are presented to show that both Gat1p and Gat2p(Sct1p) are G-3-P/dihydroxyacetone phosphate dual substrate-specific sn-1 acyltransferases. The fatty acyl specificity of Gat1p is similar to that of the mammalian microsomal G-3-P acyltransferase, as it can effectively utilize a broad range of fatty acids as acyl donors. In contrast, Gat2p(Sct1p) displayed preference toward 16-carbon fatty acids. The most notable of the altered phospholipid compositions of the gat1Δ and g at2(sct1)Δ strains are a decreased phosphatidic acid pool and an increased phosphatidylserine/phosphatidylinositol ratio. This did not appear to affect the mutants as no growth defect was found. However, null mutations of both GAT1 and GAT2(SCT1) are synthetically lethal to yeast. glycerol 3-phosphate phosphatidylcholine phosphatidylethanolamine phosphatidylserine phosphatidylinositol phosphatidic acid lysophosphatidic acid polymerase chain reaction dihydroxyacetone phosphate dithiothreitol thin layer chromatography Studies on the new roles of phospholipids as structural elements in membranes, as well as cell signaling components, continue to be at the forefront of our efforts in understanding a wide range of biological processes (1Daum G. Lees N.D. Bard M. Dickson R. Yeast. 1998; 14: 1471-1510Crossref PubMed Scopus (530) Google Scholar, 2Carman G.M. Henry S.A. Prog. Lipid Res. 1999; 38: 361-399Crossref PubMed Scopus (264) Google Scholar, 3Moolenaar W.H. J. Biol. Chem. 1995; 270: 12949-12952Abstract Full Text Full Text PDF PubMed Scopus (572) Google Scholar, 4English D. Cui Y. Siddiqui R. Chem. Phys. Lipids. 1996; 80: 117-132Crossref PubMed Scopus (158) Google Scholar). Meanwhile, there are still significant knowledge gaps with regard to various aspects of regulation of the phospholipid biosynthetic pathway (1Daum G. Lees N.D. Bard M. Dickson R. Yeast. 1998; 14: 1471-1510Crossref PubMed Scopus (530) Google Scholar, 2Carman G.M. Henry S.A. Prog. Lipid Res. 1999; 38: 361-399Crossref PubMed Scopus (264) Google Scholar). It is well established that the initial step of phospholipid biosynthesis involves the acylation of G-3-P1 at the sn-1 position by a G-3-P acyltransferase to form lysophosphatidic acid (LPA). LPA acyltransferase then catalyzes the acylation of LPA at the sn-2 position to generate phosphatidic acid (PA), which serves as a general precursor for all glycerophospholipids, including triacylglycerol in eukaryotes (5Dircks L. Sul H.S. Prog. Lipid Res. 1999; 38: 461-479Crossref PubMed Scopus (59) Google Scholar, 6Christiansen K. Biochim. Biophys. Acta. 1978; 530: 78-90Crossref PubMed Scopus (30) Google Scholar). In Escherichia coli, an integral membrane protein (plsB) is responsible for the G-3-P acyltransferase activity, and its corresponding gene has been identified (7Wilkison W.O. Bell R.M. Biochim. Biophys. Acta. 1997; 1348: 3-9Crossref PubMed Scopus (27) Google Scholar). In eukaryotic cells, multiple isoforms of G-3-P acyltransferase are present and localized in different intracellular compartments (8Dircks L.K. Sul H.S. Biochim. Biophys. Acta. 1997; 1348: 17-26Crossref PubMed Scopus (60) Google Scholar, 9Murata N. Tasaka Y. Biochim. Biophys. Acta. 1997; 1348: 10-16Crossref PubMed Scopus (92) Google Scholar). The genes corresponding to the mammalian mitochondrial and plant plastidial G-3-P acyltransferases have been isolated and characterized in detail (8Dircks L.K. Sul H.S. Biochim. Biophys. Acta. 1997; 1348: 17-26Crossref PubMed Scopus (60) Google Scholar, 9Murata N. Tasaka Y. Biochim. Biophys. Acta. 1997; 1348: 10-16Crossref PubMed Scopus (92) Google Scholar). In contrast, the eukaryotic microsomal counterpart has so far remained elusive, mainly because of the difficulties encountered in the purification of these membrane proteins and reconstitution of functional enzymes. Bakers' yeast, Saccharomyces cerevisiae, is a convenient model organism for eukaryotic lipid studies because its glycerolipid biosynthetic pathway is very similar to a wide range of species including higher plants and mammals. More than a decade ago, Tillman and Bell reported mutants deficient in the activities of G-3-P acyltransferase in S. cerevisiae (10Tillman T.S. Bell R.M. J. Biol. Chem. 1986; 261: 9144-9149Abstract Full Text PDF PubMed Google Scholar). Subsequent biochemical characterizations of one such mutant, generally known as TTA1, have yielded many new insights into lipid metabolism. It is now widely accepted that the initial step of glycerolipid biosynthesis in yeast is mediated by a G-3-P/DHAP dual substrate acyltransferase (10Tillman T.S. Bell R.M. J. Biol. Chem. 1986; 261: 9144-9149Abstract Full Text PDF PubMed Google Scholar,12Athenstaedt K. Weys S. Paltauf F. Daum G. J. Bacteriol. 1999; 181: 1458-1463Crossref PubMed Google Scholar), and that multiple isoforms of G-3-P acyltransferase are present in yeast (11Athenstaedt K. Daum G. J. Bacteriol. 1997; 179: 7611-7616Crossref PubMed Scopus (98) Google Scholar, 12Athenstaedt K. Weys S. Paltauf F. Daum G. J. Bacteriol. 1999; 181: 1458-1463Crossref PubMed Google Scholar). However, the protein and the gene corresponding to the mutation have not been identified because of the lack of an apparent selectable growth phenotype in TTA1. Based on our general interest in eukaryotic fatty acyltransferases, we pursued the identification of G-3-P acyltransferase genes after examining some of the available information on yeast mutants related to phospholipid synthesis. When the CDP-DAG pathway is suppressed by inositol in the yeast mutant ise (13Yamashita S. Oshima A. Eur. J. Biochem. 1980; 104: 611-616Crossref PubMed Scopus (63) Google Scholar), the activity of choline transporter (CTR1) becomes essential for phospholipid biosynthesis through the CDP-choline pathway (14Nikawa J. Tsukagoshi Y. Yamashita S. J. Bacteriol. 1986; 166: 328-330Crossref PubMed Google Scholar, 15Nikawa J. Hosaka K. Tsukagoshi Y. Yamashita S. J. Biol. Chem. 1990; 265: 15996-16003Abstract Full Text PDF PubMed Google Scholar). The ise ctr1 double mutant cannot grow on high inositol medium even in the presence of a choline supplement (14Nikawa J. Tsukagoshi Y. Yamashita S. J. Bacteriol. 1986; 166: 328-330Crossref PubMed Google Scholar). Such a growth defect is apparently caused by a reduced synthesis of phosphatidylcholine (PC). It was subsequently reported that a choline transporter suppressor gene, SCT1, corresponding to ORF YBL011w (also annotated as YBL03.09), when expressed via a multicopy vector, could complement the cell growth defect, which resulted from the deficiency in choline transport in ise ctr1 (16Matsushita M. Nikawa J. J. Biochem. (Tokyo). 1995; 117: 447-451Crossref PubMed Scopus (19) Google Scholar). However, SCT1 cannot suppress the growth defect of CTR1 null mutant, and overexpression of SCT1 did not appear to restore choline transport activity. It was suggested that Sct1p might stabilize the mutant form of the choline transporter (16Matsushita M. Nikawa J. J. Biochem. (Tokyo). 1995; 117: 447-451Crossref PubMed Scopus (19) Google Scholar). However, one could also envisage Sct1p as being a positive factor involved in the biosynthetic pathway leading to PC synthesis. This would appear to be a plausible explanation if a small amount of choline is available, as to be the in In the present we that the choline transporter Sct1p, by YBL011w, and a closely related protein by YKR067w, are two yeast sn-1 acyltransferases both G-3-P and A mutation in YKR067w results in a deficiency of the acyltransferase activities in the yeast mutant TTA1. in the studies of acyltransferases, identification of these two initial of the glycerolipid pathway is for understanding the regulation of phospholipid biosynthesis in yeast and it is similar in including The gene strains and the YBL011w gene strain and the strains and from The mutant was by M. Bell (10Tillman T.S. Bell R.M. J. Biol. Chem. 1986; 261: 9144-9149Abstract Full Text PDF PubMed Google Scholar). at in medium and from and its strain was respectively, to the of YBL011w and YKR067w genes. was in a reaction and of polymerase The for the of YBL011w and and and and The was as initial of at then of at for at for and at for by at for The into the of a through polymerase and an of and for the from TTA1, and and for to and The into The of the was by enzyme and designated as and expression the of and by of and with into and then into coli to the and into R.M. J. Bacteriol. 117: PubMed Google Scholar), and of the confirmed by yeast expression of GAT1 and genes from and through with and and into The of the and was by of and the into gat1Δ strain was to the R. K. in Molecular Scholar). and in of medium with and at for the to of medium and to grow the cell an was then to a of and the at for an to protein by at g for with and in with for on the was on with a The was at g for to cell and the was for enzyme of the proteins was confirmed through GAT1 and in yeast, and in of medium with at for the by at g for and in medium with and The then with of medium to a cell of at for to the protein the by at g for of the yeast the cell with of and then in and at with to R. K. in Molecular Scholar). in was at for to cell and the was for enzyme was protein and as a G-3-P acyltransferase activity was at for in a reaction 3-phosphate and The reaction was by the with of in the presence of of a with of and of the of the and J. Biochem. PubMed Scopus Google was with of of the the glycerolipid was and to for are the from at the reaction the lipid to in a of The for LPA and and J. 1978; PubMed Scopus Google Scholar). acyltransferase activity was as by and Biochem. J. PubMed Scopus Google with The reaction was by the of by with of and of The of the and was with of and the through The by with the The of in was J. 1978; PubMed Scopus Google Scholar). cell at disrupted with the of Lees M. J. Biol. Chem. Full Text PDF PubMed Google Scholar). of the phospholipids was with on and in as Bell R.M. J. Biol. Chem. Full Text PDF PubMed Google Scholar). with through a the and with acid from of the lipid species and by these the of the phospholipids for was with and to a corresponding to a and in A with and was to the of the GAT1 The yeast gene was then into the of the to generate a GAT1 The the yeast gene by two GAT1 was the as a with at and of the and The amount of the was to the strain and the More than from The the and the one disrupted GAT1 and one GAT1 identified by and of the with the strain did not in and to R. K. in Molecular Scholar). studies have that SCT1 gene is expressed in yeast. is most a membrane as it was to a of (16Matsushita M. Nikawa J. J. Biochem. (Tokyo). 1995; 117: 447-451Crossref PubMed Scopus (19) Google Scholar). revealed that Sct1p by YBL011w and a protein by YKR067w, which to Sct1p, with to of known acyltransferases Biochem. J. 1999; 38: Scopus Google Scholar). A of acid is with of the G-3-P acyltransferases from coli and the mitochondrial G-3-P acyltransferase from as in A. from and the and respectively, of G-3-P acyltransferases Biochem. J. 1999; 38: Scopus Google Scholar). The corresponding to is by a of acids that is in and The structural the yeast proteins and known membrane G-3-P acyltransferases can be further by as in Based on these we that and are for the so far sn-1 fatty The to if of the open reading YKR067w would affect G-3-P acyltransferase activity in yeast. strains with in and YKR067w from the of strains at strain displayed growth phenotype when on in was there apparent to inositol the of the open reading it was that a dramatic reduction of G-3-P activity could be even when a total of the yeast strain was for enzyme K. Weys S. Paltauf F. Daum G. J. Bacteriol. 1999; 181: 1458-1463Crossref PubMed Google Scholar). to the of the gene on G-3-P acyltransferase activities total yeast after a at in G-3-P acyltransferase activity was reduced in both gene The total G-3-P acyltransferase activity in the YBL011w strain was reduced by one in to the Disruption of YKR067w, on the a a enzyme activity at one of the our the of enzyme activity in the YKR067w gene strain is very to the G-3-P acyltransferase activity for strain not even are from different further the of these initial we if the mutation leading to the in G-3-P acyltransferase and acyltransferase activities in the mutant in YBL011w YKR067w (10Tillman T.S. Bell R.M. J. Biol. Chem. 1986; 261: 9144-9149Abstract Full Text PDF PubMed Google Scholar). The of the two genes by isolated from and its strain in both genes the S. cerevisiae The of YBL011w and YKR067w from into the the of of the and of the into a that there was no in YBL011w and the of YKR067w revealed the presence of one from to A at position in the mutant TTA1, which is to in the of acid for at acid position of the acid in the high to the of acyltransferases Biochem. J. 1999; 38: Scopus Google Scholar). This that the deficiency of acyltransferase activity in is to missense and suggested that YKR067w encodes for a G-3-P The G-3-P acyltransferase activity in is with that of the YKR067w that the mutation in TTA1, even in the form of a acid the activity of This is in with of the coli G-3-P acyltransferase, a in the acid in the from to the enzyme activity Biochem. J. 1999; 38: Scopus Google Scholar). results further the functional of these in fatty acyltransferases. it has been that the defect in mainly the acyltransferase activities of the lipid It can be that is the lipid G-3-P In with the by and Daum and K. Weys S. Paltauf F. Daum G. J. Bacteriol. 1999; 181: 1458-1463Crossref PubMed Google Scholar), we as The protein Sct1p by YBL011w, which has structural of a membrane protein (16Matsushita M. Nikawa J. J. Biochem. (Tokyo). 1995; 117: 447-451Crossref PubMed Scopus (19) Google Scholar), be localized in membrane we designated it herein as The genes corresponding to YKR067w and YBL011w GAT1 and of acyltransferases for enzyme activity has to be In an to a GAT1 and GAT2(SCT1) as well as the from into expression and into coli (plsB) strain R.M. J. Bacteriol. 117: PubMed Google Scholar). has a mutation in that to a G-3-P acyltransferase with altered a activity Bell R.M. J. Biol. Chem. 1980; Full Text PDF PubMed Google Scholar, J. Bacteriol. 1999; 181: PubMed Google Scholar). This strain been as a convenient to G-3-P acyltransferase genes for enzyme Biochem. J. 1999; 38: Scopus Google Scholar). in G-3-P acyltransferase activity in mutant GAT1 was than higher than that of the In contrast, expression of in the no enzyme activities the coli strain has a G-3-P phenotype as a of a in the apparent of the G-3-P acyltransferase for G-3-P R.M. J. Bacteriol. 117: PubMed Google Scholar, Biochem. J. 1999; 38: Scopus Google Scholar, J. Bacteriol. 1999; 181: PubMed Google Scholar). However, expression of the GAT1 both and in strain to complement In expression of the GAT2(SCT1) to be to the The growth of the gene was by a factor of when with the the have not been to in G-3-P acyltransferase activity through expression of GAT2(SCT1) in of the apparent difficulties involved in the reconstitution of enzyme activities of acyltransferases, we to a on the G-3-P acyltransferase of the gat1Δ strain to the substrate of Gat1p and Gat2p(Sct1p) with to G-3-P and The two genes expressed a multiple the of activities of G-3-P and acyltransferase of the two proteins as the fatty acyl of GAT1 resulted in a of and in G-3-P acyltransferase and acyltransferase significant in G-3-P acyltransferase and acyltransferase activities also in the gat1Δ strain GAT2(SCT1) The in the activities of G-3-P and acyltransferases indicate that Gat1p and Gat2p(Sct1p) can utilize both G-3-P and as that the two yeast sn-1 acyltransferases are G-3-P/DHAP dual substrate acyltransferases. It is also with the of and Daum K. Daum G. J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google that a of lipid that as a results in of with Gat1p to out the glycerolipid pathway in yeast lipid in Gat1p displayed the of enzyme activities with regard to G-3-P and Gat2p(Sct1p) G-3-P even was also an acid substrate specificity of acyltransferases an in stereospecific of fatty acyl in preference in to and fatty acids has also been in regulation of of fatty acids into the fatty acyl substrate of Gat1p and activities toward and the gat1Δ strain GAT1 and GAT2(SCT1), in Gat1p could utilize all fatty acyl with a activity toward In the of the fatty acyl specificity of Gat1p are similar to that of the mammalian microsomal G-3-P acyltransferase, which is also of a broad range of (8Dircks L.K. Sul H.S. Biochim. Biophys. Acta. 1997; 1348: 17-26Crossref PubMed Scopus (60) Google Scholar). In contrast, Gat2p(Sct1p) exhibited preference for fatty acids. both to fatty acids the roles and of the two acyltransferases to phospholipid the of phospholipids from the gat1Δ and strains with of the In with reported for the strain K. Weys S. Paltauf F. Daum G. J. Bacteriol. 1999; 181: 1458-1463Crossref PubMed Google Scholar), the of the pool in the gat1Δ as of total was reduced to than of that of the strain reduction of the pool in the strain was also is also a in the of and with a from in the strain to and respectively, in the gat1Δ and In of the fatty acyl substrate of the two acyltransferases, we also the fatty acid compositions of the phospholipid species in gat1Δ and The presented in can be as of Gat1p in yeast did not to have a significant on the total fatty acid of and However, a decrease in fatty acid was in and the reduction is by in both and The of Gat2p(Sct1p) fatty acid compositions in all phospholipid In the mutant and such a decrease in was by in the of fatty acid compositions of different phospholipids in and mutant of fatty not yeast the gat1Δ the in medium to a for fatty acid not in a new yeast the gat1Δ the in medium to a for fatty acid the growth and biochemical phenotype of the gat1Δ double null mutant, of GAT1 was carried out in a Subsequent that two from and all of the carried the When GAT1 was with the to generate double it that gat1Δ and are synthetically lethal to yeast. The of LPA as the and step in phospholipid synthesis has been well a understanding of the initial acylation reaction of the glycerolipid pathway in yeast and we carried out the identification of G-3-P acyltransferase genes. was on studies of the yeast mutant a mutant involved in the regulation of the phosphatidylethanolamine pathway (13Yamashita S. Oshima A. Eur. J. Biochem. 1980; 104: 611-616Crossref PubMed Scopus (63) Google Scholar), and the choline transporter mutant ctr1 (14Nikawa J. Tsukagoshi Y. Yamashita S. J. Bacteriol. 1986; 166: 328-330Crossref PubMed Google Scholar). and biochemical studies that YBL011w and YKR067w, designated in as and respectively, are genes for G-3-P acyltransferases. The ise mutant is a choline growth is by high of defect can be suppressed by the medium with choline (13Yamashita S. Oshima A. Eur. J. Biochem. 1980; 104: 611-616Crossref PubMed Scopus (63) Google Scholar). The growth defect of ise mutant in to inositol has been to be the of a dramatic decrease in the activity (13Yamashita S. Oshima A. Eur. J. Biochem. 1980; 104: 611-616Crossref PubMed Scopus (63) Google Scholar). the growth defect, cannot the decrease in the enzyme activities of by high of inositol (13Yamashita S. Oshima A. Eur. J. Biochem. 1980; 104: 611-616Crossref PubMed Scopus (63) Google Scholar), that the of choline to an in PC synthesis via the CDP-choline A choline transporter mutant, a decrease in choline and a CDP-choline pathway for PC synthesis. The ise ctr1 double mutant a growth defect when high of inositol is present in the even in the presence of choline (14Nikawa J. Tsukagoshi Y. Yamashita S. J. Bacteriol. 1986; 166: 328-330Crossref PubMed Google Scholar). it that the of a CDP-choline pathway and a pathway is the for the growth defect of ise high of was to suppress the growth defect of the ise ctr1 mutant in the presence of inositol and choline (16Matsushita M. Nikawa J. J. Biochem. (Tokyo). 1995; 117: 447-451Crossref PubMed Scopus (19) Google Scholar). However, the by which Gat2p(Sct1p) the ise and not been Gat2p(Sct1p) of a choline transporter (16Matsushita M. Nikawa J. J. Biochem. (Tokyo). 1995; 117: 447-451Crossref PubMed Scopus (19) Google a we that it might its through in the phospholipid This is with the that ctr1 apparently some of choline J. Hosaka K. Tsukagoshi Y. Yamashita S. J. Biol. Chem. 1990; 265: 15996-16003Abstract Full Text PDF PubMed Google Scholar), and that the of Gat2p(Sct1p) was in a (16Matsushita M. Nikawa J. J. Biochem. (Tokyo). 1995; 117: 447-451Crossref PubMed Scopus (19) Google Scholar). GAT2(SCT1) can its via a multicopy vector, that it most an enzyme than a protein in the CDP-choline pathway of PC synthesis (16Matsushita M. Nikawa J. J. Biochem. (Tokyo). 1995; 117: 447-451Crossref PubMed Scopus (19) Google Scholar). that Gat2p(Sct1p) and the closely related by YKR067w, G-3-P acyltransferases, in on the of in which we two similar to the of known acyltransferases Biochem. J. 1999; 38: Scopus Google Scholar). of GAT1 GAT2(SCT1) resulted in a reduction in the total cellular G-3-P acyltransferase was further by a mutation revealed in of the G-3-P acyltransferase mutant TTA1. In overexpression of the GAT1 and GAT2(SCT1) genes in the gat1Δ which has a G-3-P acyltransferase to enzyme expression of GAT1 in coli strain a our in expression of GAT2(SCT1) in coli to indicate in G-3-P acyltransferase activity, is not in a for a membrane A structural Gat1p and Gat2p(Sct1p) at the (16Matsushita M. Nikawa J. J. Biochem. (Tokyo). 1995; 117: 447-451Crossref PubMed Scopus (19) Google Scholar). that the acid the which is in acid and and is involved in of proteins (16Matsushita M. Nikawa J. J. Biochem. (Tokyo). 1995; 117: 447-451Crossref PubMed Scopus (19) Google Scholar), to the difficulties in the reconstitution of enzyme activity in However, because both and overexpression of GAT2(SCT1) in yeast results with regard to G-3-P acyltransferase activity with we it that Gat2p(Sct1p) is a of the enzyme in yeast. It be even in a in enzyme activity in the coli it is that the protein is at a in in because it to complement the G-3-P phenotype of The in the might in the reconstitution of enzyme activity for Gat1p by Studies of Tillman and Bell that the mutation in to in both G-3-P and acyltransferase activities (10Tillman T.S. Bell R.M. J. Biol. Chem. 1986; 261: 9144-9149Abstract Full Text PDF PubMed Google Scholar). lipid of TTA1, and Daum and K. Weys S. Paltauf F. Daum G. J. Bacteriol. 1999; 181: 1458-1463Crossref PubMed Google also the that G-3-P and acyltransferase activities are to a present to that both of these two sn-1 acyltransferases in yeast G-3-P and in studies with K. Weys S. Paltauf F. Daum G. J. Bacteriol. 1999; 181: 1458-1463Crossref PubMed Google Scholar), the pool is reduced in both gat1Δ and of gene to in a significant reduction of the of an in was The of fatty acid in phospholipids from the lack of of the two isoforms are generally with fatty acyl which not substrate has on fatty acid on the as a of its apparent preference toward 16-carbon fatty a in the fatty acid of The of Gat1p being the lipid G-3-P acyltransferase was from the defect revealed in TTA1. The substrate specificity of Gat1p with regard to G-3-P/DHAP is also in with the of the lipid acyltransferase reported from biochemical Studies of K. Weys S. Paltauf F. Daum G. J. Bacteriol. 1999; 181: 1458-1463Crossref PubMed Google have that in to the lipid acyltransferase, of phospholipid biosynthesis are present in both the microsomal and mitochondrial The mitochondrial sn-1 acyltransferase a of G-3-P acyltransferase to acyltransferase activity, and a acyltransferase K. Weys S. Paltauf F. Daum G. J. Bacteriol. 1999; 181: 1458-1463Crossref PubMed Google Scholar). Gat2p(Sct1p) G-3-P to it be present in the The that Gat2p(Sct1p) as a choline transporter suppressor also that it is to be localized in membrane The lethal phenotype of that Gat1p and Gat2p(Sct1p) are the if not the sn-1 acyltransferases in the This has information for efforts to the of phospholipid biosynthesis in eukaryotic and for on are for with R. and D. and of the