Phosphatidylserine Transport to the Mitochondria Is Regulated by Ubiquitination

Mitochondrial membrane biogenesis requires the interorganelle transport of phospholipids. Phosphatidylserine (PtdSer) synthesized in the endoplasmic reticulum and related membranes (mitochondria-associated membrane (MAM)) is transported to the mitochondria by unknown gene products and decarboxylated to form phosphatidylethanolamine at the inner membrane by PtdSer decarboxylase 1 (Psd1p). We have designed a screen for strains defective inPtdSer transport (pstAmutants) between the endoplasmic reticulum and Psd1p that relies on isolating ethanolamine auxotrophs in suitable (psd2Δ) genetic backgrounds. Following chemical mutagenesis, we isolated an ethanolamine auxotroph that we designatepstA1-1. Using in vivo and in vitro phospholipid synthesis/transport measurements, we demonstrate that the pstA1-1 mutant is defective in PtdSer transport between the MAM and mitochondria. The gene that complements the growth defect and PtdSer transport defect of the pstA1-1 mutant is MET30, which encodes a substrate recognition subunit of the SCF (suppressor of kinetochore protein 1, cullin,F-box) ubiquitin ligase complex. Reconstitution of different permutations of MAM and mitochondria from wild type andpstA1-1 strains demonstrates that theMET30 gene product affects both organelles. These data provide compelling evidence that interorganelle PtdSer traffic is regulated by ubiquitination. Mitochondrial membrane biogenesis requires the interorganelle transport of phospholipids. Phosphatidylserine (PtdSer) synthesized in the endoplasmic reticulum and related membranes (mitochondria-associated membrane (MAM)) is transported to the mitochondria by unknown gene products and decarboxylated to form phosphatidylethanolamine at the inner membrane by PtdSer decarboxylase 1 (Psd1p). We have designed a screen for strains defective inPtdSer transport (pstAmutants) between the endoplasmic reticulum and Psd1p that relies on isolating ethanolamine auxotrophs in suitable (psd2Δ) genetic backgrounds. Following chemical mutagenesis, we isolated an ethanolamine auxotroph that we designatepstA1-1. Using in vivo and in vitro phospholipid synthesis/transport measurements, we demonstrate that the pstA1-1 mutant is defective in PtdSer transport between the MAM and mitochondria. The gene that complements the growth defect and PtdSer transport defect of the pstA1-1 mutant is MET30, which encodes a substrate recognition subunit of the SCF (suppressor of kinetochore protein 1, cullin,F-box) ubiquitin ligase complex. Reconstitution of different permutations of MAM and mitochondria from wild type andpstA1-1 strains demonstrates that theMET30 gene product affects both organelles. These data provide compelling evidence that interorganelle PtdSer traffic is regulated by ubiquitination. phosphatidylserine ethanolamine phosphatidylethanolamine phosphatidylcholine endoplasmic reticulum mitochondria-associated membrane PtdSer decarboxylase 1 and 2, respectively PtdSer synthase 1 synthetic complete lactate 1-acyl-2-(N-4-nitrobenzo-2-oxa-1,3-diazole)-aminocaproyl-phosphatidyl[1′-14C]serine 4-morpholineethanesulfonic acid suppressor of kinetochore protein 1, cullin, F-box Mitochondrial membrane assembly requires the import of proteins and lipids. Whereas much is known regarding mitochondrial protein import (1Schatz G. Dobberstein B. Science. 1996; 271: 1519-1526Crossref PubMed Scopus (922) Google Scholar, 2Koehler C.M. FEBS Lett. 2000; 476: 27-31Crossref PubMed Scopus (92) Google Scholar), little is known at the molecular level about mitochondrial import of phospholipids (3Voelker D.R. Biochim. Biophys. Acta. 2000; 1486: 97-107Crossref PubMed Scopus (73) Google Scholar). Mitochondrial lipid import is thought to be essential for biogenesis of this organelle in all eukaryotic organisms. In addition to importing lipids, mitochondria also export significant quantities of PtdEtn to other organelles. Elucidation of the mechanisms of lipid import into and export out of mitochondria and the gene products that participate in the process remains a fundamental problem of cell biology and biochemistry. Our approach to understanding mitochondrial lipid traffic has been to focus on aminoglycerophospholipid transport events in the de novo biosynthetic pathway of Saccharomyces cerevisiae. Fig. 1 depicts the synthesis of aminoglycerophospholipids in S. cerevisiae. PtdSer1 is synthesized from serine and CDP-diacylglycerol by PtdSer synthase 1 (Pss1p) in the ER and MAM (4Gaigg B. Simbeni R. Hrastnik C. Paltauf F. Daum G. Biochim. Biophys. Acta. 1995; 1234: 214-220Crossref PubMed Scopus (168) Google Scholar). Subsequently, PtdSer is transported to the site of PtdSer decarboxylase 1 (Psd1p) in the inner mitochondrial membrane, where it is converted to phosphatidylethanolamine (PtdEtn) (5Trotter P.J. Pedretti J. Voelker D.R. J. Biol. Chem. 1993; 268: 21416-21424Abstract Full Text PDF PubMed Google Scholar, 6Achleitner G. Gaigg B. Krasser A. Kainersdorfer E. Kohlwein S. Perktold A. Zellnig G. Daum G. Eur. J. Biochem. 1999; 264: 545-553Crossref PubMed Scopus (243) Google Scholar, 7Vance J.E. Shiao Y. Anticancer Res. 1996; 16: 1333-1340PubMed Google Scholar, 8Kuchler K. Daum G. Paltauf F. J. Bacteriol. 1986; 165: 901-910Crossref PubMed Google Scholar). This routing of PtdSer appears true for all eukaryotes. In yeast, PtdSer can also be decarboxylated at the locus of PtdSer decarboxylase 2 (Psd2p) in the vacuole and Golgi compartments (9Trotter P.J. Pedretti J. Yates R. Voelker D.R. J. Biol. Chem. 1995; 270: 6071-6080Abstract Full Text Full Text PDF PubMed Scopus (135) Google Scholar, 10Trotter P.J. Voelker D.R. J. Biol. Chem. 1995; 270: 6062-6070Abstract Full Text Full Text PDF PubMed Scopus (206) Google Scholar). We have chosen to name the PtdSertransport pathways PSTA and PSTB to designate traffic to the mitochondria and the Golgi/vacuole, respectively. PtdEtn can be exported from the loci of Psd1p and Psd2p, and we have named these pathways PEEA and PEEB (denoting PtdEtnexport), respectively. The exported PtdEtn can be for membrane synthesis it can be in the ER by and to form phosphatidylcholine F. Kohlwein The and of the Scholar). PtdEtn and can also be synthesized the pathways from the ethanolamine (3Voelker D.R. Biochim. Biophys. Acta. 2000; 1486: 97-107Crossref PubMed Scopus (73) Google Scholar). PtdEtn and thought to be essential for S. growth in that (5Trotter P.J. Pedretti J. Voelker D.R. J. Biol. Chem. 1993; 268: 21416-21424Abstract Full Text PDF PubMed Google Scholar, B. S. J. Bacteriol. PubMed Google Scholar, Voelker J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google Scholar, R. R. Daum G. Biol. PubMed Scopus Google Scholar). In S. Psd1p is the PtdSer of the PtdEtn in the of an ethanolamine P.J. Voelker D.R. J. Biol. Chem. 1995; 270: 6062-6070Abstract Full Text Full Text PDF PubMed Scopus (206) Google Scholar). Whereas PtdEtn by Psd1p appears to be for mitochondrial it is also for other a cell mutant defective in transport of PtdSer has cell PtdEtn in a defect in K. J. Biol. 2000; PubMed Scopus Google Scholar, K. S. A. 1999; PubMed Scopus Google Scholar). PtdEtn is also the of ethanolamine to synthesis is essential for cell J. Biol. Chem. Full Text PDF PubMed Google Scholar, Biochem. 1993; PubMed Google Scholar). PtdEtn a in S. by to Y. Y. Y. E. Y. 2000; PubMed Scopus Google Scholar). the of PtdSer is transported from the ER to the inner mitochondrial membrane for PtdEtn is also an of for other mitochondrial of PtdSer from the to mitochondria is thought to of the membranes of the G. Gaigg B. Krasser A. Kainersdorfer E. Kohlwein S. Perktold A. Zellnig G. Daum G. Eur. J. Biochem. 1999; 264: 545-553Crossref PubMed Scopus (243) Google Scholar, D.R. J. Biol. Chem. 1993; 268: Full Text PDF PubMed Google Scholar, Y. B. J.E. Biochem. J. PubMed Scopus (73) Google Scholar, G. J.E. J. Biol. Chem. 1995; 270: Full Text Full Text PDF PubMed Scopus Google Scholar, J. Biol. 1995; PubMed Scopus Google Scholar, F. F. C. J. Biol. Chem. 1993; 268: Full Text PDF PubMed Google Scholar). The of is transport is by MAM and proteins (4Gaigg B. Simbeni R. Hrastnik C. Paltauf F. Daum G. Biochim. Biophys. Acta. 1995; 1234: 214-220Crossref PubMed Scopus (168) Google Scholar, Y. B. J.E. Biochem. J. PubMed Scopus (73) Google Scholar, G. J.E. J. Biol. Chem. 1995; 270: Full Text Full Text PDF PubMed Scopus Google Scholar). protein gene product has been that ER to mitochondria membrane transport of PtdSer between these organelles. the of to transport in the PSTA these transport and the gene that complements In this we the of a ethanolamine in a genetic the of a demonstrate the of a defect in the transport of PtdSer to the mitochondria. The defect is by the gene an essential protein in that has a in the of for and growth from S. and The from synthesized from and CDP-diacylglycerol (5Trotter P.J. Pedretti J. Voelker D.R. J. Biol. Chem. 1993; 268: 21416-21424Abstract Full Text PDF PubMed Google Scholar). and CDP-diacylglycerol from from strains in of of of of of to to a of the of strains in lactate by and B. and A. Scholar). The of on a The from a mutant from The isolated an ethanolamine auxotroph from the PubMed Scopus Google Scholar). and from the in this and and also from the mutant The in and by strains in synthetic lactate ethanolamine to and in serine to an in a of 2 by at for and by the addition of acid to a of of by (5Trotter P.J. Pedretti J. Voelker D.R. J. Biol. Chem. 1993; 268: 21416-21424Abstract Full Text PDF PubMed Google Scholar, P.J. Pedretti J. Yates R. Voelker D.R. J. Biol. Chem. 1995; 270: 6071-6080Abstract Full Text Full Text PDF PubMed Scopus (135) Google and by on the by the by to lipid into of of of the by mitochondria B. and A. from to in lactate and ethanolamine at mitochondrial in and for protein protein of the membrane by A. Biochim. Google Scholar). and Psd1p of the mitochondrial (5Trotter P.J. Pedretti J. Voelker D.R. J. Biol. Chem. 1993; 268: 21416-21424Abstract Full Text PDF PubMed Google Scholar, 10Trotter P.J. Voelker D.R. J. Biol. Chem. 1995; 270: 6062-6070Abstract Full Text Full Text PDF PubMed Scopus (206) Google Scholar). synthesis and transport into by G. Gaigg B. Krasser A. Kainersdorfer E. Kohlwein S. Perktold A. Zellnig G. Daum G. Eur. J. Biochem. 1999; 264: 545-553Crossref PubMed Scopus (243) Google a mitochondria in to a protein of 1 The of of and of C. to in a the by of of in an by the addition of of of and of by and to the by the by to and The of of of of The and a in and by on The lipid 1-acyl-2-(N-4-nitrobenzo-2-oxa-1,3-diazole)-aminocaproyl-phosphatidyl[1′-14C]serine to transport between the and inner mitochondrial The synthesized D.R. J. Biol. Chem. Full Text PDF PubMed Google Scholar). mitochondria on B. and A. Scholar). The transport of mitochondrial protein and of in a of The at for in a 2 for The by the addition of of the a and The from the that on the by mitochondria isolated from of of mitochondria and MAM by G. Gaigg B. Krasser A. Kainersdorfer E. Kohlwein S. Perktold A. Zellnig G. Daum G. Eur. J. Biochem. 1999; 264: 545-553Crossref PubMed Scopus (243) Google Scholar). mitochondria in on a of in in in B. The at for 1 at an from the of the in and for at at MAM from the of the in and for 1 at at mitochondrial and MAM in and and a isolated mitochondria and MAM for protein and into by G. Gaigg B. Krasser A. Kainersdorfer E. Kohlwein S. Perktold A. Zellnig G. Daum G. Eur. J. Biochem. 1999; 264: 545-553Crossref PubMed Scopus (243) Google a mitochondria also for of the membrane by In a MAM and mitochondria at protein of and respectively. in the of lipid mitochondrial to in synthetic lactate ethanolamine at The in synthetic lactate and at for for mitochondrial mitochondria by the of and B. and A. Scholar). from of mitochondrial in of of of The of of of of The and a by on The acid by and the acid by by and into the of G. S. PubMed Scopus Google Scholar). from and pstA1-1 strains in lactate the of and B. and A. Scholar). import the of and S. G. J.E. Scholar). The Psd1p a from a The from a proteins synthesized in vitro the in the of The protein isolated mitochondria in the of in an import 1 and 2 to The also 2 and and for at The proteins from the by for at The of Following the the mitochondria by in and for The The and 1 The proteins a of protein import from The gene to from the of K. C. 2000; Full Text Full Text PDF PubMed Scopus Google Scholar). The gene in strains and by of In we the strains and from and respectively. The strains in and The by and acid to the by for The on and by The by in and The in and at to the cell in an of 1 and an of cell to the and the in a for by at at The to on The the and a of and strains that have on Psd1p for the of PtdEtn and synthesis in the of ethanolamine Fig. We that in PtdSer import into and PtdEtn export from the locus of Psd1p in the inner mitochondrial membrane ethanolamine for growth in genetic mitochondrial phospholipid transport we and for ethanolamine auxotrophs on lactate a to of of the ethanolamine of which and an by genetic and of the a for ethanolamine for growth in at in Fig. In the of the and In the of the to the The growth of the is the in the and of little growth in synthetic lactate of ethanolamine In is an ethanolamine auxotroph in synthetic at in Fig. the growth defect of in synthetic lactate at a for these a of ethanolamine a at a that for the ethanolamine the is The of the mutant strains and in PtdEtn the growth of the mutant and strains to in The and in at an of at by the ethanolamine mutant a defect in the of in of the into by of the lipid the of PtdSer and the of in PtdEtn a of PtdSer transport to and import into the mitochondria. Fig. that the mutant has a of in PtdEtn and in PtdSer to the of the also in both the mutant and the the in significant of PtdEtn and The PtdEtn a substrate for the and in the synthesis of The to the PtdSer and PtdEtn can also the that is for the synthesis of a of this the of the appears P.J. Voelker D.R. J. Biol. Chem. 1995; 270: 6062-6070Abstract Full Text Full Text PDF PubMed Scopus (206) Google Scholar). The defective PtdEtn in a of in by of mutant of In genetic that the strains and these that PtdSer is at the locus of Psd1p in the inner mitochondrial membrane to cell Psd1p of the PtdEtn in the of we that a defect in PtdSer transport to mitochondria to a in and mitochondrial of we the phospholipid of mitochondria by B. and A. Scholar). that the mitochondrial PtdEtn of the mutant is about of the in the and of the mutant the in the PtdEtn These data the cell and a defect in PtdSer transport to the mitochondria have PtdEtn mitochondrial for the phospholipid of mutant and the for of phospholipids from in a mitochondrial for the phospholipid of mutant and the for of phospholipids from We an in vitro transport in which a mitochondrial MAM is in the of These provide for an of into is to a of the of into PtdEtn for an Fig. an of in PtdSer and a of in PtdEtn in to the The in vitro the cell is to the in a substrate for we in This that the in PtdEtn of the mutant is to PtdEtn to Fig. that the mitochondrial of the mutant have Psd1p and that to the The in of the mutant to of the PtdEtn the in PtdEtn is to Psd1p we that the defect between these biosynthetic these data demonstrate that the mutant is in PtdSer from the MAM to the locus of Psd1p in the inner mitochondria we have this mutant from have and Psd1p mitochondria MAM isolated from and mutant strains by The for and and the of into lipid The for Psd1p the and the product on 2 for the and for the mutant for in The defect in lipid traffic in the pstA1-1 mutant between the MAM and the mitochondrial membrane between the and inner mitochondrial by K. S. A. 1999; PubMed Scopus Google have a cell mutant defective in PtdSer transport between mitochondrial the gene has been In D.R. J. Biol. Chem. Full Text PDF PubMed Google Scholar), we a to the mitochondrial membrane the lipid and import into the inner The data in Fig. the of of the transport of the lipid between the mitochondrial membranes organelles. The of import of between the and the mutant These demonstrate that the in mutant between the mitochondrial membranes between the MAM and the mitochondrial defect in PtdSer transport to the mitochondria be to the of the mitochondria for we that mutant strains mitochondria of In Fig. the of a of mitochondria The mitochondria from a between and In the on the of a In to the the a of mitochondria between and The of the to the of the mitochondria. The of mitochondria is The phospholipid of the mitochondrial from is of and that of the pstA1-1 is of which the in These data the a defect in lipid traffic to the mitochondria. The data also demonstrate that mitochondrial of at different can be in both the and mutant in both lipid traffic to the mitochondria and organelle we also the import of proteins into mitochondria on B. and A. Scholar). these we an of from the of subunit of the mitochondrial and J. PubMed Scopus Google that is to the import of In we the import and of The proteins a S. G. J.E. Scholar), and the and membrane import of the proteins in Fig. The for is into the mitochondria and to form in both and pstA1-1 The of import into mutant mitochondria is of that for mitochondria. The for Psd1p is also into the mitochondria and to the inner membrane of both and mutant of the mitochondrial and the inner membrane of Psd1p and The data in Fig. the of the subunit of Psd1p and that the import into mutant mitochondria at of the for mitochondria. These provide evidence that the pstA1-1 mutant has a defect in the of protein import into the mitochondria. the in protein and phospholipid import into the it is also to that in protein import protein in the in PtdSer import the of PtdEtn and The to which to screen a for that the ethanolamine of for ethanolamine from into the growth on other growth on The that the of pstA1-1 ethanolamine and of the into that the ethanolamine to pstA1-1 mutant Fig. that a the can the growth defect of a pstA1-1 mutant in of The gene encodes a substrate subunit of SCF ubiquitin ligase Biol. 1999; PubMed Scopus Google Scholar). an for the protein subunit and for R. Y. Biol. 1995; PubMed Scopus Google Scholar, C. 1996; Full Text Full Text PDF PubMed Scopus Google Scholar). demonstrate that can the PtdSer transport defect in we vitro transport mitochondria on a Fig. on can the of into PtdEtn the andpstA1-1 the in vivo and in vitro data that wild type can both the ethanolamine and We also the defect in cell growth and lipid traffic we strains is an We a A. R. J. 2000; PubMed Scopus Google and gene it The on at to on at of the the growth defect at We also isolated mitochondria from on lactate that been to the and the mutant an of in PtdSer and a defect in the of PtdEtn in Fig. These about the of in PtdSer traffic to the mitochondria. We also the mitochondrial in the and the in Fig. to the the a mitochondrial The also the of mitochondria in the wild type the in defective PtdSer and mitochondrial to that has mitochondria of mitochondria from wild type and mutant strains in lactate at The mitochondria to at for 1 in an The the strains and the and of the on the of we the from a pstA1-1 the R. PubMed Scopus Google Scholar). We the by and for ethanolamine the to a the on both which in a of for at acid This the of that in substrate is that this the of the and substrate The to the of The substrate for ubiquitin ligase is a of in K. C. 2000; Full Text Full Text PDF PubMed Scopus Google Scholar, A. R. Full Text Full Text PDF PubMed Scopus Google Scholar). We the of in to in pstA1-1 and and wild type of of is in Fig. A. In the of and the SCF to of The be to gene and growth the appears other growth K. C. 2000; Full Text Full Text PDF PubMed Scopus Google Scholar, A. R. Full Text Full Text PDF PubMed Scopus Google Scholar). In of of addition of in wild type in Fig. B. In the the of and and The pstA1-1 mutant also in addition the of and The wild type for the also and In significant at also significant of the at and of In addition to in we in lactate these the that the In lactate we that the of and of In also of of the that the of is in the pstA1-1 these we that a defect in ubiquitination. The in vivo defect in is growth of the pstA1-1 in lactate In the we genetic in which we of a of lipid the of the pstA1-1 we These data it that a of lipid These data also that a of lipid These the that for be and to lipid has that PtdSer can be transported from MAM to mitochondria in a both G. Gaigg B. Krasser A. Kainersdorfer E. Kohlwein S. Perktold A. Zellnig G. Daum G. Eur. J. Biochem. 1999; 264: 545-553Crossref PubMed Scopus (243) Google Scholar). We have this to the pstA1-1 transport defect is the MAM the mitochondria. MAM and mitochondria from a and the wild type on of wild type MAM in wild type mutant mitochondria and mutant MAM in wild type mutant mitochondria. the synthesis and transport of PtdSer a The of PtdSer and the of in PtdEtn a of PtdSer transport from the MAM to the mitochondria. the of the data the of in Fig. These data that the transport defect in the cell and the mitochondrial is also in the MAM and mitochondria type of PtdSer to the mutant about The wild type MAM the defect in a mutant mitochondria. In wild type mitochondria the defect in a mutant These demonstrate that the transport defect is mitochondria MAM appears to in both organelles. these we that has a on transport in both mitochondria and In this we the of a auxotroph the for a mutant a defect in PtdSer transport from the MAM to the mitochondria. This is of a genetic approach in Fig. 1 that we to in lipid The is the that we have in the PSTA that we aminoglycerophospholipid to the mitochondria. The pstA1-1 mutant for on a lactate This to a to strains that an for mitochondria. The of the pstA1-1 be by the of to synthesis of the this lipid This both the for of PtdEtn in the and the essential of PtdEtn in that has been Voelker J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google Scholar, R. R. Daum G. Biol. PubMed Scopus Google Scholar). the pstA1-1 is an the level and of PtdEtn synthesis is in these of PtdEtn and synthesis be the we have in this genetic We that the of PtdEtn to be by the pathway to PtdEtn by Psd1p to be and by the mitochondria. In this we the that an isolated A. R. J. 2000; PubMed Scopus Google Scholar), that is to the pstA1-1 a it is a that it is an auxotroph on at of the PtdSer traffic between isolated from that the in lipid synthesis and of In that PtdSer synthesis in the MAM and transport to the the pstA1-1 a of PtdSer and in the of this the defect in lipid traffic is it is to a growth in the cell and a in This lipid transport defect is also in the The of in to be to the mitochondrial membrane and lipid traffic to the inner mitochondrial membrane D.R. J. Biol. Chem. Full Text PDF PubMed Google Scholar). Our demonstrate that the defect in the mutant is between the mitochondrial membranes between the MAM and the mitochondrial the of the transport to events between the MAM and mitochondria the from that that a significant of the mitochondria from pstA1-1 has The defect in PtdSer transport to the mitochondria the of the organelle to This in that the mitochondria to for the PtdSer transport defect by the import synthesis of other phospholipids. The is an in the of the mitochondria isolated from the mutant This defect is also in These data that both the and mutant to have mitochondria of different is also that the pstA1-1 has a mitochondrial also the the the of lipid between the MAM and mitochondria is have that proteins on the of both membranes participate in the process G. Gaigg B. Krasser A. Kainersdorfer E. Kohlwein S. Perktold A. Zellnig G. Daum G. Eur. J. Biochem. 1999; 264: 545-553Crossref PubMed Scopus (243) Google Y. B. J.E. Biochem. J. PubMed Scopus (73) Google Scholar). evidence has also been to that proteins participate in the lipid of these has been Biochem. PubMed Scopus Google Scholar, J. J. Biol. PubMed Scopus Google Scholar). and have of between the MAM and mitochondria in the of PtdSer (4Gaigg B. Simbeni R. Hrastnik C. Paltauf F. Daum G. Biochim. Biophys. Acta. 1995; 1234: 214-220Crossref PubMed Scopus (168) Google Scholar, 6Achleitner G. Gaigg B. Krasser A. Kainersdorfer E. Kohlwein S. Perktold A. Zellnig G. Daum G. Eur. J. Biochem. 1999; 264: 545-553Crossref PubMed Scopus (243) Google D.R. J. Biol. Chem. 1993; 268: Full Text PDF PubMed Google Scholar, Y. B. J.E. Biochem. J. PubMed Scopus (73) Google Scholar, G. J.E. J. Biol. Chem. 1995; 270: Full Text Full Text PDF PubMed Scopus Google Scholar, J. Biol. 1995; PubMed Scopus Google Scholar, F. F. C. J. Biol. Chem. 1993; 268: Full Text PDF PubMed Google Scholar). The gene that complements the pstA1-1 in growth and lipid traffic is The gene encodes a protein an and that substrate for a of SCF ubiquitin Biol. 1999; PubMed Scopus Google R. Y. Biol. 1995; PubMed Scopus Google Scholar). The is the site of of the of the ligase C. 1996; Full Text Full Text PDF PubMed Scopus Google Scholar). The in The pstA1-1 in the of the in a between the and We that this the recognition of and ubiquitination. of the data of PtdSer transport to the mitochondria by the process of ubiquitination. the level at which ubiquitin ligase lipid traffic is is to at that 1996; PubMed Scopus Google Scholar), Science. PubMed Scopus Google Scholar), K. C. 2000; Full Text Full Text PDF PubMed Scopus Google Scholar, A. R. Full Text Full Text PDF PubMed Scopus Google Scholar), and Biol. PubMed Scopus Google Scholar, Full Text Full Text PDF PubMed Scopus Google Scholar). for have been K. C. 2000; Full Text Full Text PDF PubMed Scopus Google Scholar, A. R. J. 2000; PubMed Scopus Google Scholar), the Science. PubMed Scopus Google Scholar), and PubMed Scopus Google Scholar). to of the K. C. 2000; Full Text Full Text PDF PubMed Scopus Google Scholar, A. R. J. 2000; PubMed Scopus Google and of a Science. PubMed Scopus Google Scholar). The is an that is PubMed Scopus Google Scholar). is the substrate for ubiquitin we also mutant defective in In in Fig. we that in the pstA1-1 mutant in these we that also be defective in and other We also designed a genetic to a of lipid traffic of In this we and for the an we that a of PtdSer In these also a for a of lipid is also to an in membrane traffic a for protein and Biol. PubMed Scopus Google Scholar). a for in lipid traffic of membrane for the assembly of that of and membranes MAM and and lipid In addition to of has protein to mitochondrial and Using a genetic suppressor and J. Biol. 1999; PubMed Scopus Google the ubiquitin ligase an essential of mitochondrial and ubiquitin ligase appears to a in the and of mitochondria. The has also been in R. J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google Scholar), and protein at the S. J. Biol. PubMed Scopus Google Scholar), and in B. A. G. S. A. 2000; PubMed Scopus Google Scholar). Our also that the of in PtdSer transport to mitochondria is to this The PtdSer transport in these to the site of of Using permutations of of wild type MAM and we the to both organelles. We this to that in both MAM and to this be of proteins on both organelles. be to the of is In we have isolated a mutant defective in PtdSer traffic between the MAM and the mitochondria. The the PtdEtn the phospholipid and the of the The of the in both the MAM and mitochondria and by the which encodes a of SCF ubiquitin These a for interorganelle phospholipid We of for the and for mitochondrial protein import of of and the strains about and The by de