Influenza Viruses Select Ordered Lipid Domains during Budding from the Plasma Membrane

During the budding of enveloped viruses from the plasma membrane, the lipids are not randomly incorporated into the envelope, but virions seem to have a lipid composition different from the host membrane. Here, we have analyzed lipid assemblies in three different viruses: fowl plague virus (FPV) from the influenza virus family, vesicular stomatitis virus (VSV), and Semliki Forest virus (SFV). Analysis of detergent extractability of proteins, cholesterol, phosphoglycerolipids, and sphingomyelin in virions showed that FPV contains high amounts of detergent-insoluble complexes, whereas such complexes are largely absent from VSV or SFV. Cholesterol depletion from the viral envelope by methyl-β-cyclodextrin results in increased solubility of sphingomyelin and of the glycoproteins in the FPV envelope. This biochemical behavior suggests that so-called raft-lipid domains are selectively incorporated into the influenza virus envelope. The “fluidity” of the FPV envelope, as measured by the fluorescence polarization of diphenylhexatriene, was significantly lower than compared with VSV or SFV. Furthermore, influenza virus hemagglutinin incorporated into the envelope of recombinant VSV was largely detergent-soluble, indicating the depletion of raft-lipid assemblies from this membrane. The results provide a model for lipid selectivity during virus budding and support the view of lipid rafts as cholesterol-dependent, ordered domains in biological membranes. During the budding of enveloped viruses from the plasma membrane, the lipids are not randomly incorporated into the envelope, but virions seem to have a lipid composition different from the host membrane. Here, we have analyzed lipid assemblies in three different viruses: fowl plague virus (FPV) from the influenza virus family, vesicular stomatitis virus (VSV), and Semliki Forest virus (SFV). Analysis of detergent extractability of proteins, cholesterol, phosphoglycerolipids, and sphingomyelin in virions showed that FPV contains high amounts of detergent-insoluble complexes, whereas such complexes are largely absent from VSV or SFV. Cholesterol depletion from the viral envelope by methyl-β-cyclodextrin results in increased solubility of sphingomyelin and of the glycoproteins in the FPV envelope. This biochemical behavior suggests that so-called raft-lipid domains are selectively incorporated into the influenza virus envelope. The “fluidity” of the FPV envelope, as measured by the fluorescence polarization of diphenylhexatriene, was significantly lower than compared with VSV or SFV. Furthermore, influenza virus hemagglutinin incorporated into the envelope of recombinant VSV was largely detergent-soluble, indicating the depletion of raft-lipid assemblies from this membrane. The results provide a model for lipid selectivity during virus budding and support the view of lipid rafts as cholesterol-dependent, ordered domains in biological membranes. glycosylphosphatidylinositol detergent-insoluble glycolipid-enriched complex hemagglutinin fowl plague virus vesicular stomatitis virus Semliki Forest virus bovine hamster kidney sphingomyelin phosphatidylcholine phosphatidylethanolamine polyacrylamide gel electrophoresis methyl-β-cyclodextrin diphenylhexatriene dipalmitoylphosphatidylcholine. The hypothesis that lipids from the plasma membrane are not randomly included into the viral envelope, but that budding could occur from specialized domains of the membrane, was put forward several years ago (1Lenard J. Compans R.W. Biochim. Biophys. Acta. 1974; 344: 51-94Crossref PubMed Scopus (118) Google Scholar, 2Pessin J.E. Glaser M. J. Biol. Chem. 1980; 255: 9044-9050Abstract Full Text PDF PubMed Google Scholar). Comparing the lipid composition of various viruses with the composition of the host cell membrane, clear cut differences have been reported, although caution has to be exercised because viruses can be isolated practically pure, whereas plasma membrane fractions cannot be (2Pessin J.E. Glaser M. J. Biol. Chem. 1980; 255: 9044-9050Abstract Full Text PDF PubMed Google Scholar, 3Renkonen O. Kääräinen L. Simons K. Gahmberg C.G. Virology. 1971; 46: 318-326Crossref PubMed Scopus (79) Google Scholar, 4Aloia R.C. Tian H. Jensen F.C. Proc. Natl. Acad. Sci. U. S. A. 1993; 90: 5181-5185Crossref PubMed Scopus (376) Google Scholar). Thus, the role of lipid domains has remained controversial and has not so far been given functional significance. New insights into the mechanisms of domain formation in biological membranes have come from the analysis of detergent-resistant membrane fractions (5Brown D.A. Rose J.K. Cell. 1992; 68: 533-544Abstract Full Text PDF PubMed Scopus (2618) Google Scholar). Recent evidence suggests that laterally associating sphingolipids and cholesterol form small ordered domains, called rafts, which are resistant to extraction with Triton X-100 at 4 °C. These domains can incorporate specific proteins and function as platforms for intracellular sorting and signal transduction events (6Simons K. Ikonen E. Nature. 1997; 387: 569-572Crossref PubMed Scopus (8157) Google Scholar, 7Brown D.A. London E. Biochem. Biophys. Res. Commun. 1997; 240: 1-7Crossref PubMed Scopus (464) Google Scholar). Recently, the concentration of GPI1-anchored proteins in microdomains has been confirmed in living cells by biophysical and biochemical methods without the use of detergents (8Friedrichson T. Kurzchalia T. Nature. 1998; 394: 802-805Crossref PubMed Scopus (480) Google Scholar, 9Varma R. Mayor S. Nature. 1998; 394: 798-801Crossref PubMed Scopus (1031) Google Scholar). However, when GPI-anchored proteins on the apical surface of epithelial cells were analyzed, no such concentration could be observed (10Kenworthy A.K. Edidin M. J. Cell Biol. 1998; 142: 69-84Crossref PubMed Scopus (404) Google Scholar). The reason for this discrepancy is not known, yet one explanation could be that this membrane represents a continuous raft domain in contrast to the plasma membrane of nonpolarized cells, where raft domains would be noncontinuous (6Simons K. Ikonen E. Nature. 1997; 387: 569-572Crossref PubMed Scopus (8157) Google Scholar, 10Kenworthy A.K. Edidin M. J. Cell Biol. 1998; 142: 69-84Crossref PubMed Scopus (404) Google Scholar, 11Vaz W.L.C. Almeida P.F.F. Curr. Opin. Struct. Biol. 1993; 3: 482-488Crossref Scopus (71) Google Scholar). Recent studies have shown that cholesterol promotes the detergent insolubility of GPI-anchored proteins or transmembrane proteins both in cellular membranes and in artificial lipid vesicles (12Cerneus D.P. Ueffing E. Posthuma G. Strous G.J. van der Ende A. J. Biol. Chem. 1993; 268: 3150-3155Abstract Full Text PDF PubMed Google Scholar, 13Hanada K. Nishijima M. Akamatsu Y. Pagano R.E. J. Biol. Chem. 1995; 270: 6254-6260Abstract Full Text Full Text PDF PubMed Scopus (191) Google Scholar, 14Scheiffele P. Roth M.G. Simons K. EMBO J. 1997; 16: 5501-5508Crossref PubMed Scopus (571) Google Scholar, 15Schroeder R.J. Ahmed S.N. Zhu Y. London E. Brown D. J. Biol. Chem. 1998; 273: 1150-1157Abstract Full Text Full Text PDF PubMed Scopus (375) Google Scholar). Lipids recovered in detergent-insoluble glycolipid-enriched complexes (DIGs) were shown to have higher melting temperatures than the average lipids from the plasma membrane, suggesting that raft-domains might be formed from lipids with preferentially saturated acyl chains (16Schroeder R. London E. Brown D. Proc. Natl. Acad. Sci. U. S. A. 1994; 91: 12130-12134Crossref PubMed Scopus (638) Google Scholar). Interestingly, for artificial lipid vesicles detergent insolubility could be correlated with the formation of a liquid-ordered phase in the membrane (15Schroeder R.J. Ahmed S.N. Zhu Y. London E. Brown D. J. Biol. Chem. 1998; 273: 1150-1157Abstract Full Text Full Text PDF PubMed Scopus (375) Google Scholar, 17Ahmed S.N. Brown D.A. London E. Biochemistry. 1997; 36: 10944-10953Crossref PubMed Scopus (615) Google Scholar), suggesting that phase separation might be the basis for the formation of insoluble lipid rafts in biological membranes (7Brown D.A. London E. Biochem. Biophys. Res. Commun. 1997; 240: 1-7Crossref PubMed Scopus (464) Google Scholar, 18Rietveld A. Simons K. Biochim. Biophys. Acta. 1998; 1376: 467-479Crossref PubMed Scopus (454) Google Scholar). Also, specific viral glycoproteins have been described to be associated with raft domains during transport to the cell surface. Both the influenza virus neuraminidase and hemagglutinin are recovered in DIGs after entering the Golgi complex (19Skibbens J.E. Roth M.G. Matlin K.S. J. Cell Biol. 1989; 108: 821-832Crossref PubMed Scopus (178) Google Scholar, 20Kundu A. Avalos R.T. Sanderson C.M. Nayak D.P. J. Virol. 1996; 70: 6508-6515Crossref PubMed Google Scholar). Efficient surface transport of influenza virus HA requires cholesterol, and the protein stays raft-associated at the plasma membrane (14Scheiffele P. Roth M.G. Simons K. EMBO J. 1997; 16: 5501-5508Crossref PubMed Scopus (571) Google Scholar, 21Keller P. Simons K. J. Cell Biol. 1998; 140: 1357-1367Crossref PubMed Scopus (472) Google Scholar). Here we used membranes of baby hamster kidney (BHK) cells and the viral envelopes of influenza fowl plague virus (FPV), vesicular stomatitis virus (VSV), and Semliki Forest virus (SFV) as model systems to analyze the formation of detergent-resistant lipid domains in a biological membrane. Our results demonstrate that the viruses contain lipid raft assemblies to a very different extent. Furthermore, we show that in all of the membranes analyzed cholesterol is required for the formation of detergent-insoluble lipid complexes and that such complexes are highly ordered. Our results therefore support a model in which cholesterol promotes the formation of lipid domains that become selectively incorporated into the influenza envelope. BHK cells (strain CCL10, American Culture Collection) were maintained in G-MEM (5% FCS, 10% tryptosephosphate 10 mm Hepes, 2 mm glutamine, 100 units/ml penicillin, 100 μg/ml streptomycin) in 5% CO2 at 37 °C in a humidified incubator. Virus stocks of influenza virus (strain A/FPV), VSV, SFV, and the recombinant VSV-HA (22Kretzschmar E. Buonocore L.M.J. Schnell M.J. Rose J.K. J. Virol. 1997; 71: 5982-5989Crossref PubMed Google Scholar) were produced as described K.S. Simons K. Cell. Full Text PDF PubMed Scopus Google Scholar, M. A. Simons K. EMBO J. PubMed Scopus Google Scholar). BHK cells, a membrane was as described P. R. H. M. Simons K. J. Cell Biol. 1992; PubMed Scopus Google Scholar). cells were with a a was to and with and for 4 4 °C in a membranes were recovered from the cells on one were for 4 with of in or for with of in G-MEM without analyze membranes after viral the cells were and as the analysis of proteins, and the viruses were in BHK the of cells from three were and in 10 viruses were to the cells in 10 2 mm glutamine, 100 units/ml penicillin, 100 μg/ml streptomycin) for The was and by the was and to cell 4 The was on of a in mm mm of of and 10 of 10% in a a at and 4 the was in and on in a 4 in a the was and the virus was in at 4 °C. from 10 of viral protein for FPV and VSV and for SFV. viruses were produced the in the cells were with of in with cells were for 4 with of in 10 mm Hepes, 2 100 and 100 μg/ml cells were with and viruses were and as described with cells on were with of for in G-MEM without cells were and viruses were and of virus or membrane with a lipid than were with of Triton mm mm mm on for the was in a in a for at and 4 °C. in and fractions were analyzed by lipids from and fractions were to and J. Biochem. PubMed Scopus Google Scholar) and analyzed by on with as a lipids were by and by analysis amounts of were by virus 10 of protein were with of on for were to by the of of with of in and of were for 2 in a 4 and fractions were from the of the were from the fractions by the of one of and analyzed by and with methyl-β-cyclodextrin were for at 37 °C in mm and 10 μg/ml with were on and for in a 4 were by in a 4 and was and a of were as described (16Schroeder R. London E. Brown D. Proc. Natl. Acad. Sci. U. S. A. 1994; 91: 12130-12134Crossref PubMed Scopus (638) Google Scholar). Virus or lipid vesicles were in 100 of and of in was were for in the and fluorescence was measured at °C in with at 4 vesicles were by of 2 of from or in results were viruses or lipid vesicles at of μg/ml and at of to without or without the of viruses was raft domains in different the viruses were produced in BHK and isolated by The were as by and The detergent solubility of the viral glycoproteins was analyzed by extraction with Triton X-100 on and in virus HA was to as observed (14Scheiffele P. Roth M.G. Simons K. EMBO J. 1997; 16: 5501-5508Crossref PubMed Scopus (571) Google Scholar), whereas the VSV or the glycoproteins in the of the indicating that were by the detergent of a with rafts in the viral envelope is specific for influenza viruses and not a Cholesterol is in detergent-insoluble fractions from cellular membranes (5Brown D.A. Rose J.K. Cell. 1992; 68: 533-544Abstract Full Text PDF PubMed Scopus (2618) Google Scholar). therefore compared the Triton solubility of cholesterol in the different viral envelopes and the host cell membrane. BHK cells were with and viruses were produced and The membranes were with Triton X-100 on and and in and fractions was by by this at be a membrane from BHK cells was and the cholesterol solubility showed differences the viruses analyzed the influenza viruses of the cholesterol was in VSV and in with the BHK membrane for the plasma membrane, and Golgi membranes T. R. J. Biol. Cell. 1997; PubMed Scopus Google cholesterol solubility in the influenza virus envelope is and increased in VSV and SFV. is to that the cholesterol solubility in membranes from BHK cells was not significantly in with cells not used to analyze the extractability of cholesterol in the different viral contrast to with of membranes and of from the J. Biol. Chem. 1995; 270: Full Text Full Text PDF PubMed Scopus Google Scholar, U. G. Biochemistry. 1995; PubMed Scopus Google Scholar). influenza viruses and VSV were with of cholesterol was from the VSV envelope mm of cholesterol from VSV but from the influenza virus be that practically no cholesterol was observed when the extraction were not During the the viral remained and not show as by and The extractability of cholesterol by from the envelope was to be compared with the VSV and FPV the results were not explanation from the analysis of the contrast to FPV and VSV, the of the was cholesterol and the were by the This might a of the membrane and in of the at higher of has been observed when virions were produced in cells M. T. M. J. Cell Biol. 1998; 140: PubMed Scopus Google Scholar). However, cholesterol in influenza viruses is in a detergent-resistant whereas this is not the for VSV and analysis of viral after cholesterol FPV and VSV and and were without or with mm and for at 37 °C and by for 4 The were observed in after The observed differences in cholesterol extractability could from the of raft domains into the viral envelopes to this viruses were produced in BHK and at 4 °C. Lipids from the and insoluble fractions were by and by The lipids in the BHK membrane were phosphatidylethanolamine phosphatidylcholine and sphingomyelin 4 and were largely by Triton a of the was insoluble for the cholesterol no in the Triton X-100 solubility of lipids were observed after viral not However, the solubility in the viral envelopes showed in influenza viruses 5% of the could be after detergent or could be from VSV or SFV, 4 analyze the cholesterol of the lipid membranes or virus were with mm this concentration because the of of the cholesterol but the and results in a of lipids from the not of was cholesterol-dependent, of the membranes in increased both in the FPV and VSV envelopes and in the BHK membrane 4 Also, the solubility of in the FPV envelope was increased cholesterol cholesterol is not required for the of proteins with but for the formation of detergent-insoluble lipid assemblies in a biological membrane. This that DIGs are not complexes from insoluble but that different lipid is required to form a detergent-resistant X-100 solubility of cholesterol and in BHK membranes and viral without or after cholesterol depletion by mm of of lipid at after Triton X-100 extraction is from at three with three are given with in a The of lipid at after Triton X-100 extraction is from at three with three are given with with artificial lipid vesicles that membranes in the liquid-ordered phase and GPI-anchored proteins incorporated into membranes are insoluble in Triton X-100 at 4 °C (16Schroeder R. London E. Brown D. Proc. Natl. Acad. Sci. U. S. A. 1994; 91: 12130-12134Crossref PubMed Scopus (638) Google Scholar, 17Ahmed S.N. Brown D.A. London E. Biochemistry. 1997; 36: 10944-10953Crossref PubMed Scopus (615) Google Scholar). was therefore that DIGs isolated from biological membranes might be from domains in the liquid-ordered phase (7Brown D.A. London E. Biochem. Biophys. Res. Commun. 1997; 240: 1-7Crossref PubMed Scopus (464) Google Scholar). polarization of the incorporated into membranes has been used as a of acyl vesicles detergent-insoluble lipids showed significantly higher fluorescence polarization than lipid vesicles from lipid the of ordered domains as a basis for insolubility (16Schroeder R. London E. Brown D. Proc. Natl. Acad. Sci. U. S. A. 1994; 91: 12130-12134Crossref PubMed Scopus (638) Google Scholar). cellular membranes are viral envelopes provide a to analyze fluorescence polarization in a biological lipid was incorporated into the envelopes of VSV, and SFV, the influenza virus showed the fluorescence whereas the were for VSV and vesicles by were all viral membranes show a higher fluorescence polarization than the lipid which are in the the vesicles are in the gel phase and show a very high fluorescence polarization The for the FPV envelope are suggesting a high of in this envelope and the hypothesis that DIGs are from ordered domains in biological membranes. the envelope showed the VSV and FPV indicating a although to the detergent solubility of the lipids highly ordered lipid complexes were not this can be by the that is which is different from the viruses FPV and have a very high protein and the of the and proteins are by Cell. 1995; Full Text PDF PubMed Scopus Google Scholar, T. U. P. 1997; PubMed Scopus Google Scholar). These protein assemblies might the ordered of the membrane, by the lipid of fluorescence in viruses or lipid vesicles at polarization of in viruses or lipid vesicles was are from at three and were in a polarization of in viruses or lipid vesicles was are from at three and were detergent-resistant membranes can be formed by lipids (16Schroeder R. London E. Brown D. Proc. Natl. Acad. Sci. U. S. A. 1994; 91: 12130-12134Crossref PubMed Scopus (638) Google Scholar). However, is not proteins lipid might be required to or such domains in biological membranes. used a recombinant vesicular stomatitis which influenza virus HA into the envelope (22Kretzschmar E. Buonocore L.M.J. Schnell M.J. Rose J.K. J. Virol. 1997; 71: 5982-5989Crossref PubMed Google to analyze the detergent solubility of HA in the lipid of BHK cells were with and viruses were The of HA to VSV in the envelope was as E. Buonocore L.M.J. Schnell M.J. Rose J.K. J. Virol. 1997; 71: 5982-5989Crossref PubMed Google Scholar, were with Triton X-100 on and in the and were analyzed by or with HA or VSV both glycoproteins were largely by the no amounts of HA were in after Triton X-100 extraction with Furthermore, cholesterol in the VSV-HA envelope was in Triton X-100 indicating that the of HA in a viral envelope is not to insoluble domains and that the lipid incorporated into VSV and FPV during budding are have analyzed detergent-resistant lipid complexes in cellular membranes and different viral The use of the viral envelope as a model membrane has several artificial lipid the envelope is from the cellular plasma membrane, has a lipid Furthermore, is the membrane contains proteins that have a on the membrane Our results demonstrate that the three viral envelopes contain lipid raft domains to a very different as by the detergent solubility of proteins and artificial lipid was that such detergent-insoluble complexes are from lipids in the liquid-ordered or gel phase (15Schroeder R.J. Ahmed S.N. Zhu Y. London E. Brown D. J. Biol. Chem. 1998; 273: 1150-1157Abstract Full Text Full Text PDF PubMed Scopus (375) Google Scholar, 17Ahmed S.N. Brown D.A. London E. Biochemistry. 1997; 36: 10944-10953Crossref PubMed Scopus (615) Google Scholar). of that influenza viruses contain lipids in a to the liquid-ordered cholesterol, and phosphatidylcholine in the influenza envelope are detergent-insoluble to a extent. cholesterol is required for the insolubility of the have that cholesterol is required for detergent insolubility of HA in cells as in the isolated virions (14Scheiffele P. Roth M.G. Simons K. EMBO J. 1997; 16: 5501-5508Crossref PubMed Scopus (571) Google Scholar). The cholesterol of and insolubility that cholesterol is required for the formation of insoluble complexes in biological membranes than for a specific HA and the This is with the for cholesterol for the formation of ordered domains in the membrane Proc. Natl. Acad. Sci. U. S. A. PubMed Scopus Google Scholar). the fluorescence polarization demonstrate that acyl chains in the influenza virus envelope are highly whereas acyl chains in the VSV envelope are lipid detergent-resistant membranes in the gel phase can be formed of cholesterol, by the of high amounts of (15Schroeder R.J. Ahmed S.N. Zhu Y. London E. Brown D. J. Biol. Chem. 1998; 273: 1150-1157Abstract Full Text Full Text PDF PubMed Scopus (375) Google Scholar). the lipid composition of the membranes in cells to be such that cholesterol is to the formation of the liquid-ordered whereas a gel phase not in cell membranes T. M. M. G. E. Biochim. Biophys. Acta. 1993; PubMed Scopus Google Scholar). However, has been observed that cells can lipid acyl chains when cells, on the when cellular cholesterol are to M. C.M. J. Biol. Chem. Full Text PDF PubMed Google Scholar). cells of lipid composition to the formation of laterally domains in the of cholesterol as has been observed for However, the of such domains have not been Biophys. Biophys. Chem. PubMed Scopus Google Scholar). envelopes have a very high is therefore in to the lipid proteins on the membrane virus HA contains in domain a that is required for the with lipid raft domains (14Scheiffele P. Roth M.G. Simons K. EMBO J. 1997; 16: 5501-5508Crossref PubMed Scopus (571) Google Scholar, S. H. Roth M.G. J. Cell Biol. 1998; 142: PubMed Scopus Google Scholar). Also, the of HA might to the detergent because a the with the Roth M.G. J. Virol. 1992; PubMed Google Scholar) is and K. Both with the lipid and might the of the However, the that HA incorporated into the VSV envelope was suggests that this membrane contain lipids in ordered phase and that the of HA is not to such a detergent-resistant the VSV and influenza viruses membranes with different lipid composition from the plasma membrane. The cholesterol to in the envelopes of influenza VSV, and to be (1Lenard J. Compans R.W. Biochim. Biophys. Acta. 1974; 344: 51-94Crossref PubMed Scopus (118) Google Scholar, 3Renkonen O. Kääräinen L. Simons K. Gahmberg C.G. Virology. 1971; 46: 318-326Crossref PubMed Scopus (79) Google Scholar, P. L. Glaser M. Biochemistry. 1995; PubMed Scopus Google Scholar). sphingolipids and saturated are to the formation of raft domains (15Schroeder R.J. Ahmed S.N. Zhu Y. London E. Brown D. J. Biol. Chem. 1998; 273: 1150-1157Abstract Full Text Full Text PDF PubMed Scopus (375) Google R. London E. Brown D. Proc. Natl. Acad. Sci. U. S. A. 1994; 91: 12130-12134Crossref PubMed Scopus (638) Google Scholar), lipids might be preferentially incorporated into influenza the a analysis of the lipid and acyl chains in the different viral envelopes this analysis might the of lipids without the use of has been shown that raft domains in the plasma membrane are small and but that can of lipid or protein (8Friedrichson T. Kurzchalia T. Nature. 1998; 394: 802-805Crossref PubMed Scopus (480) Google Scholar, 9Varma R. Mayor S. Nature. 1998; 394: 798-801Crossref PubMed Scopus (1031) Google Scholar, T. P. P. Simons K. J. Cell Biol. 1998; PubMed Scopus Google Scholar). proteins could rafts into domains in the liquid-ordered the and of the complexes are by raft domains, of raft and protein P. P. H. Simons K. Ikonen E. J. Cell Biol. 1998; 140: PubMed Scopus Google Scholar). rafts could be by proteins to the of the domains S. P. Simons K. J. Cell Biol. 1998; 142: PubMed Scopus Google Scholar). that lipids in cellular membranes are in in which specific protein can the of rafts, to or of domains in the liquid-ordered on the of the of domains in the liquid-ordered phase could of the membrane R. Biophys. J. 1993; Full Text PDF PubMed Scopus Google Scholar). with this form on the cell surface but are when cholesterol is D. J. Res. 1998; Full Text Full Text PDF PubMed Google Scholar). of a liquid-ordered phase might budding of influenza viruses from the plasma membrane. this the membrane is whereas in the is The of the might on the of the specific proteins have shown that lipids in the influenza virus envelope are in ordered and ordered in the VSV envelope. This suggests that influenza virus is from raft domains in the plasma membrane. VSV, fluorescence has the formation of domains during the budding Both the and the protein were shown to of lipid the membrane P. L. Glaser M. Biochemistry. 1995; PubMed Scopus Google Scholar, P. Glaser P. Biochemistry. 1994; PubMed Scopus Google Scholar). the lipid composition of the VSV envelope was shown to from the host cell membrane, indicating of specific lipid (2Pessin J.E. Glaser M. J. Biol. Chem. 1980; 255: 9044-9050Abstract Full Text PDF PubMed Google Scholar). influenza a of the lipid and the acyl chains in the envelope and the host cell membrane has not been The of raft domains into the viral envelope of influenza virus has been observed that of HA by with raft T. P. P. Simons K. J. Cell Biol. 1998; PubMed Scopus Google Scholar). proteins with raft can be to the raft without with the influenza protein T. P. P. Simons K. J. Cell Biol. 1998; PubMed Scopus Google Scholar). has been a that influenza viruses in which the of both glycoproteins have been form H. J. EMBO J. 1997; 16: PubMed Scopus Google Scholar). This could be by the influenza proteins the rafts with the that the proteins laterally with this would to of cellular role for raft domains during virus is by the that the domain of influenza HA is required for both into the envelope and raft (14Scheiffele P. Roth M.G. Simons K. EMBO J. 1997; 16: 5501-5508Crossref PubMed Scopus (571) Google Scholar, S. H. Roth M.G. J. Cell Biol. 1998; 142: PubMed Scopus Google Scholar, Roth M.G. J. Virol. 1993; PubMed Google Scholar). lipid domains might be at of to the of cellular proteins and to specific of the viral for cell and for and during the polarization J. K. Rose for the recombinant VSV-HA for of a VSV-HA and for on the