Previous Article | Next Article 
Journal of Virology, May 2000, p. 4891-4893, Vol. 74, No. 10
0022-538X/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.
Cell-Dependent Requirement of Human
Immunodeficiency Virus Type 1 gp41 Cytoplasmic Tail for Env
Incorporation into Virions
Hirofumi
Akari,
Tomoharu
Fukumori, and
Akio
Adachi*
Department of Virology, The University of
Tokushima School of Medicine, Tokushima 770-8503, Japan
Received 8 November 1999/Accepted 16 February 2000
 |
ABSTRACT |
Growth kinetics in lymphocytic H9 and M8166 cells of two mutants of
human immunodeficiency virus type 1 (HIV-1) with deleted gp41
cytoplasmic tails were examined. While the mutant viruses designated
CTdel-44 and CTdel-144 were able to grow in M8166 cells, they were
unable to grow in H9 cells. Transfection and single-round infectivity
assays demonstrated that they are defective in the early phase of viral
replication in H9 cells. Analysis of the mutant virions revealed
drastically reduced incorporation of Env gp120 (compared with the
incorporation of wild-type virions) in H9 cells but normal
incorporation in M8166 cells. These results indicate that the HIV-1
cytoplasmic tail of gp41 determines virus infectivity in a
cell-dependent manner by affecting incorporation of Env into virions
and suggest the involvement of a host cell factor(s) in the Env incorporation.
| |
TEXT |
The Env glycoprotein of human
immunodeficiency virus type 1 (HIV-1) consists of a complex of surface
subunit gp120 and transmembrane subunit gp41, which are proteolytic
products of the gp160 precursor encoded by the env gene. In
HIV-1 infection, the gp120-gp41 complex interacts with CD4 and a batch
of chemokine receptors, and a fusion peptide and an N-terminal
ectodomain of gp41 dissociated from gp120 promote fusion between viral
and target cell membranes (6). The gp41 comprises two other
functional domains, i.e., the transmembrane subunit and cytoplasmic
domains. The gp41 cytoplasmic tail (CT) regions of HIV-1 and the other
primate immunodeficiency viruses are unusually long compared with those
of the other retroviruses (11). The CT regions of HIV-1 and
HIV-2 are generally around 150 amino acid residues in length; in
contrast, those of avian and murine leukemia viruses are typically 20 to 30 residues long. The CT region of HIV-1 contains a number of
functional domains: a tyrosine-based motif in the N-terminus as a
signal for the sorting and trafficking of Env (4); two
amphipathic motifs, which form an alpha-helix and bind calmodulin
(15, 17) and which are responsible for induction of
apoptosis in cells (12); and a C-terminal region important
for viral infectivity and Env incorporation into virions (5, 7, 8,
10, 15, 18, 20). During our mutational analysis of the HIV-1
genome, we have noticed that some mutants, including those with altered
CTs, exhibit cell-dependent growth properties (2, 13,
16; our unpublished results). In this report, we have
biologically and biochemically characterized the CT mutants and
demonstrated that the gp41 CT is a critical determinant for producing
cell-dependent virion infectivity.
To obtain input viruses to determine growth potentials of CT mutants in
lymphocytic cells, HeLa cells were transfected with proviral DNA clones
by the calcium phosphate coprecipitation method, and
cell-free solutions of viruses were prepared 48 h posttransfection as previously described (1, 16). Proviral clones used
here were wild-type (wt) pNL432 (1), its CT mutants CTdel-44
(previously referred as pNL-Hp) (2) and CTdel-144 (a
generous gift of Eric Freed, National Institutes of Health [NIH])
(7), an env-negative mutant pNL-Kp
(2), and a vif-negative mutant pNL-Nd (2, 16). CTdel-44 and CTdel-144 lack 44 and 144 C-terminal amino acids of Env gp41, respectively. The vif mutant virus
NL-Nd, which displays a cell-dependent growth phenotype
(16), was used as a control. Lymphocytic H9 and M8166
cells are nonpermissive and permissive for the NL-Nd virus,
respectively. H9 and M8166 cells were infected with each virus and were
monitored for virus production in the culture supernatants by
32P-based reverse transcriptase (RT) assay (19).
As shown in Fig. 1, H9 cells were not
productively infected by NL-Nd, CTdel-44, or CTdel-144 virus. In
contrast, in M8166 cells, these viruses grew to various extents. While
wt and NL-Nd viruses grew in a similar manner, CTdel-44 and CTdel-144
viruses showed delayed growth kinetics. CTdel-144 grew especially
poorly. These results indicated that HIV-1 gp41 CT is essential for
virus replication in H9 cells but not in M8166 cells.
View larger version (24K):
[in this window]
[in a new window]
|
FIG. 1.
Growth kinetics of wt and mutant viruses in H9 and M8166
cells. Viruses were prepared from HeLa cells transfected with pNL432
(WT), pNL-Nd (vif mutant [Nd]), CTdel-44, or CTdel-144.
Cells (106) were infected with 5 × 105 RT
units of viruses. RT production in the culture supernatants was
monitored at intervals.
|
|
To determine which step of the viral replication cycle in H9 cells is
affected by the truncated gp41, pNL432, and pNL-Nd, CT mutants were
directly transfected into H9 cells by electroporation (3).
Levels of virus production in the culture supernatants at 24 h
postelectroporation were determined by Gag p24 enzyme-linked immunosorbent assay (ELISA) (Cellular Products, Buffalo, N.Y.). No
major difference in the p24 level was observed (Table
1), and it appeared that the late
replication phase of the CT mutants in H9 cells as monitored by virus
production (Gag p24) is normal. The single-round infectivity of the
viruses produced in H9 and M8166 cells was then examined by
multinuclear activation of galactosidase inhibitor (MAGI) assay
(14). As shown in Fig. 2,
CTdel-44, CTdel-144, and NL-Nd viruses produced in H9 cells
demonstrated reduced infectivity, while those obtained from M8166 cells
exhibited a level of infectivity comparable with that of wt virus. From
these results, it was concluded that the two CT mutant viruses produced
in H9 cells are defective in the early stage of viral replication cycle
and suggested that the virions of the CT mutants released from H9 cells
are abnormal.
View larger version (16K):
[in this window]
[in a new window]
|
FIG. 2.
Infectivity of wt and mutant viruses. Single-round
infectivity of viruses derived from H9 and M8166 cells electroporated
with pNL432 (WT), pNL-Nd (vif mutant [Nd]), pNL-Kp
(env mutant [Kp]), CTdel-44 (44), or CTdel-144 (144) was
monitored by MAGI assay. Infectivity was determined by counting blue
foci of X-Gal-treated MAGI cells 2 days after inoculation of viruses.
Average and standard deviation of three independent experiments are
shown.
|
|
To examine virion proteins of the CT mutants, viruses were harvested
from electroporated H9 and M8166 cells and were concentrated by
ultracentrifugation through 20% sucrose cushion at 20,000 × g for 2 h at 4°C (3). The prepared virion
lysates were then analyzed by Western blotting assay (3).
The lysates containing an equal amount of the viral antigen as judged
by p24 ELISA were subjected to electrophoresis through sodium dodecyl
sulfate gradient (4 to 20%) polyacrylamide gels. The separated
proteins were blotted onto nitrocellulose membranes, were treated with
antibodies to HIV-1 proteins, and were visualized by using an ECL
system (Amersham, Little Chalfont, Buckinghamshire, United Kingdom).
The antisera to Env gp160 and RT were provided by M. Page through the
AIDS Research and Reference Reagent Program, Division of AIDS, National Institute of Allergy and Infectious Diseases, NIH. The anti-p24/p55 Gag
monoclonal antibody was obtained from Cosmobio (Tokyo, Japan). As shown
in Fig. 3, the level of gp120 was much
lower in CTdel-44 and CTdel-144 virions from H9 cells than in wt and
NL-Nd virions, whereas the level was comparable in all M8166-derived
virions. Figure 3 also shows no obvious differences in the amounts of
Gag and RT or in the levels of their processing among the virions derived from H9 and M8166 cells. Protein profiles of wt and mutant virions prepared from transfected HeLa cells were similar to those of
virions from transfected M8166 cells (data not shown). To further address this issue, the expression of Env within cells electroporated with various clones was similarly monitored. As shown in Fig. 4, the expression level of Env was
comparable among clone-transfected H9 and M8166 cells. In addition,
syncytia formation was similarly observed in the H9 cells transfected
with the clones. This observation suggested that the precursor of the
mutant Env was processed into biologically active mature proteins and
that these proteins were expressed on the surface of the cells as
previously reported (9). These data indicated that CTdel-44
and CTdel-144 produced in H9 cells but not in M8166 cells are defective
for Env incorporation into virions.
View larger version (67K):
[in this window]
[in a new window]
|
FIG. 3.
Analysis of virion proteins by Western blotting. The
lysates of virions prepared from H9 (A to C) and M8166 (D to F) cells
electroporated with pNL432 (WT), pNL-Nd (vif mutant [Nd]),
CTdel-44, CTdel-144, or pUC19 (control) were analyzed by Western
blotting with a sheep anti-Env gp160 antiserum (A and D), a mouse
anti-p24 monoclonal antibody (B and E), and a sheep anti-RT antiserum
(C and F).
|
|
View larger version (67K):
[in this window]
[in a new window]
|
FIG. 4.
Analysis of viral proteins expressed in cells by Western
blotting. The lysates of H9 (A and B) and M8166 (C and D) cells
electroporated with pNL432 (WT), pNL-Nd (vif mutant [Nd]),
CTdel-44, CTdel-144, or pUC19 (control) were analyzed by Western
blotting with a sheep anti-Env gp160 antiserum (A and C) and a mouse
anti-p24 monoclonal antibody (B and D).
|
|
The results presented here strongly suggest that HIV-1 gp41 CT plays a
critical role during virus assembly and entry in the virus replication
cycle in a cell-dependent way. The key finding is the
producer-cell-dependent role of the gp41 CT in Env incorporation into
virions (Fig. 3). In the absence of gp41 CT, HIV-1 virions produced in
certain cell types virtually lack Env gp120 and are defective for
initiating the next round of the virus replication cycle. In normal
virus assembly, functional association of an unknown cell factor(s)
with some domain in the C-terminal 44 amino acid residues of gp41 is important.
Although H9 and M8166 cells are nonpermissive and permissive,
respectively, for both of the vif and CT mutants, we have
recently demonstrated that the function of Vif is unrelated to Env
(3). Further study is needed to ascertain the molecular
basis for the cell-dependent functional role of HIV-1 gp41 CT, and the
identification of the cell factor(s) responsible for Env incorporation
is critically required.
| |
ACKNOWLEDGMENTS |
We thank Eric O. Freed for providing a plasmid clone. The antisera
to Env gp160 and RT (from M. Page) were obtained through the AIDS
Research and Reference Reagent Program, Division of AIDS, NIAID, NIH.
We also thank Kazuko Yoshida for editorial assistance.
This work was supported by grants-in-aid for AIDS research from the
Ministry of Education, Science, Sports, and Culture of Japan and from
the Ministry of Health and Welfare of Japan and by a grant-in-aid for
biomedical research from the Uehara Memorial Foundation.
| |
ADDENDUM |
While the manuscript was being reviewed, Murakami and Freed
published similar results (15a).
| |
FOOTNOTES |
*
Corresponding author. Mailing address: Department of
Virology, The University of Tokushima School of Medicine, 3 Kuramoto, Tokushima 770-8503, Japan. Phone: 81-88-633-7078. Fax: 81-88-633-7080. E-mail: adachi{at}basic.med.tokushima-u.ac.jp.
| |
REFERENCES |
| 1.
|
Adachi, A.,
H. E. Gendelman,
S. Koenig,
T. Folks,
R. Willey,
A. Rabson, and M. A. Martin.
1986.
Production of acquired immunodeficiency syndrome-associated retrovirus in human and nonhuman cells transfected with an infectious molecular clone.
J. Virol.
59:284-291[Abstract/Free Full Text].
|
| 2.
|
Adachi, A.,
N. Ono,
H. Sakai,
K. Ogawa,
R. Shibata,
T. Kiyomasu,
H. Masuike, and S. Ueda.
1991.
Generation and characterization of the human immunodeficiency virus type 1 mutants.
Arch. Virol.
117:45-58[CrossRef][Medline].
|
| 3.
|
Akari, H.,
T. Uchiyama,
T. Fukumori,
S. Iida,
A. H. Koyama, and A. Adachi.
1999.
Pseudotyping HIV-1 by vesicular stomatitis virus G protein does not reduce the cell-dependent requirement of Vif for optimal infectivity: functional difference between Vif and Nef.
J. Gen. Virol.
80:2945-2949[Abstract/Free Full Text].
|
| 4.
|
Boge, M.,
S. Wyss,
J. S. Bonifacino, and M. Thali.
1998.
A membrane proximal tyrosine-based signal mediated internalization of the HIV-1 envelope glycoprotein via interaction with the AP-2 clathrin adaptor.
J. Biol. Chem.
273:15773-15778[Abstract/Free Full Text].
|
| 5.
|
Dubay, J. W.,
S. J. Roberts,
B. H. Hahn, and E. Hunter.
1992.
Truncation of the human immunodeficiency virus type 1 transmembrane glycoprotein cytoplasmic domain blocks virus infectivity.
J. Virol.
66:6616-6625[Abstract/Free Full Text].
|
| 6.
|
Freed, E. O., and M. A. Martin.
1995.
The role of human immunodeficiency virus type 1 envelope glycoproteins in virus infection.
J. Biol. Chem.
270:23883-23886[Free Full Text].
|
| 7.
|
Freed, E. O., and M. A. Martin.
1995.
Virion incorporation of envelope glycoproteins with long but not short cytoplasmic tails is blocked by specific, single amino acid substitutions in the human immunodeficiency virus type 1 matrix.
J. Virol.
69:1984-1989[Abstract].
|
| 8.
|
Freed, E. O., and M. A. Martin.
1996.
Domains of the human immunodeficiency virus type 1 matrix and gp41 cytoplasmic tail required for envelope incorporation into virions.
J. Virol.
70:341-351[Abstract].
|
| 9.
|
Freed, E. O.,
D. J. Myers, and R. Risser.
1989.
Mutational analysis of the cleavage sequence of the human immunodeficiency virus type 1 envelope glycoprotein precursor gp160.
J. Virol.
63:4670-4675[Abstract/Free Full Text].
|
| 10.
|
Gabuzda, D. H.,
A. Lever,
E. Terwilliger, and J. Sodroski.
1992.
Effects of deletions in the cytoplasmic domain on biological functions of human immunodeficiency virus type 1 envelope glycoproteins.
J. Virol.
66:3306-3315[Abstract/Free Full Text].
|
| 11.
|
Hunter, E., and R. Swanstrom.
1990.
Retrovirus envelope glycoproteins.
Curr. Top. Microbiol. Immunol.
157:187-253[Medline].
|
| 12.
|
Ishikawa, H.,
M. Sasaki,
S. Noda, and Y. Koga.
1998.
Apoptosis induction by the binding of the carboxyl terminus of human immunodeficiency virus type 1 gp160 to calmodulin.
J. Virol.
72:6574-6580[Abstract/Free Full Text].
|
| 13.
|
Kawamura, M.,
R. Shimano,
R. Inubushi,
H. Akari, and A. Adachi.
1998.
Early function of HIV-1 Gag proteins is cell-dependent.
Biochem. Biophys. Res. Commun.
248:899-903[CrossRef][Medline].
|
| 14.
|
Kimpton, J., and M. Emerman.
1992.
Detection of replication-competent and pseudotyped human immunodeficiency virus with a sensitive cell line on the basis of activation of an integrated  -galactosidase gene.
J. Virol.
66:2232-2239[Abstract/Free Full Text].
|
| 15.
|
Mammano, F.,
E. Kondo,
J. Sodroski,
A. Bukovsky, and H. G. Göttlinger.
1995.
Rescue of human immunodeficiency virus type 1 matrix protein mutants by envelope glycoproteins with short cytoplasmic domains.
J. Virol.
69:3824-3830[Abstract].
|
| 15a.
|
Murakami, T., and E. O. Freed.
2000.
The long cytoplasmic tail of gp41 is required in a cell type-dependent manner for HIV-1 envelope glycoprotein incorporation into virions.
Proc. Natl. Acad. Sci. USA
97:343-348[Abstract/Free Full Text].
|
| 16.
|
Sakai, H.,
R. Shibata,
J.-I. Sakuragi,
S. Sakuragi,
M. Kawamura, and A. Adachi.
1993.
Cell-dependent requirement of human immunodeficiency virus type 1 Vif protein for maturation of virus particles.
J. Virol.
67:1663-1666[Abstract/Free Full Text].
|
| 17.
|
Srinivas, S. K.,
R. V. Srinivas,
G. M. Anantharamaiah,
R. W. Compans, and J. P. Segreat.
1993.
Cytosolic domain of the human immunodeficiency virus envelope glycoproteins binds to calmodulin and inhibits calmodulin-regulated proteins.
J. Biol. Chem.
268:22895-22899[Abstract/Free Full Text].
|
| 18.
|
Wilk, T.,
T. Pfeiffer, and V. Bosch.
1992.
Retained in vitro infectivity and cytopathogenicity of HIV-1 despite truncation of the C-terminal tail of the env gene product.
Virology
189:167-177[CrossRef][Medline].
|
| 19.
|
Willey, R. L.,
D. H. Smith,
L. A. Lasky,
T. S. Theodore,
P. L. Earl,
B. Moss,
D. J. Capon, and M. A. Martin.
1998.
In vitro mutagenesis identifies a region within the envelope gene of the human immunodeficiency virus that is critical for infectivity.
J. Virol.
62:139-147.
|
| 20.
|
Yu, X.,
X. Yuan,
M. A. McLane,
T.-H. Lee, and M. Essex.
1993.
Mutations in the cytoplasmic domain of human immunodeficiency virus type 1 transmembrane protein impair the incorporation of Env proteins into mature virions.
J. Virol.
67:213-221[Abstract/Free Full Text].
|
Journal of Virology, May 2000, p. 4891-4893, Vol. 74, No. 10
0022-538X/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.
This article has been cited by other articles:
-
Beaumont, E., Vendrame, D., Verrier, B., Roch, E., Biron, F., Barin, F., Mammano, F., Brand, D.
(2009). Matrix and Envelope Coevolution Revealed in a Patient Monitored since Primary Infection with Human Immunodeficiency Virus Type 1. J. Virol.
83: 9875-9889
[Abstract]
[Full Text]
-
Chen, P., Hubner, W., Spinelli, M. A., Chen, B. K.
(2007). Predominant Mode of Human Immunodeficiency Virus Transfer between T Cells Is Mediated by Sustained Env-Dependent Neutralization-Resistant Virological Synapses. J. Virol.
81: 12582-12595
[Abstract]
[Full Text]
-
Waheed, A. A., Ablan, S. D., Roser, J. D., Sowder, R. C., Schaffner, C. P., Chertova, E., Freed, E. O.
(2007). HIV-1 escape from the entry-inhibiting effects of a cholesterol-binding compound via cleavage of gp41 by the viral protease. Proc. Natl. Acad. Sci. USA
104: 8467-8471
[Abstract]
[Full Text]
-
Lambele, M., Labrosse, B., Roch, E., Moreau, A., Verrier, B., Barin, F., Roingeard, P., Mammano, F., Brand, D.
(2007). Impact of Natural Polymorphism within the gp41 Cytoplasmic Tail of Human Immunodeficiency Virus Type 1 on the Intracellular Distribution of Envelope Glycoproteins and Viral Assembly. J. Virol.
81: 125-140
[Abstract]
[Full Text]
-
Lopez-Verges, S., Camus, G., Blot, G., Beauvoir, R., Benarous, R., Berlioz-Torrent, C.
(2006). Tail-interacting protein TIP47 is a connector between Gag and Env and is required for Env incorporation into HIV-1 virions. Proc. Natl. Acad. Sci. USA
103: 14947-14952
[Abstract]
[Full Text]
-
Davis, M. R., Jiang, J., Zhou, J., Freed, E. O., Aiken, C.
(2006). A Mutation in the Human Immunodeficiency Virus Type 1 Gag Protein Destabilizes the Interaction of the Envelope Protein Subunits gp120 and gp41. J. Virol.
80: 2405-2417
[Abstract]
[Full Text]
-
Yuste, E., Johnson, W., Pavlakis, G. N., Desrosiers, R. C.
(2005). Virion Envelope Content, Infectivity, and Neutralization Sensitivity of Simian Immunodeficiency Virus. J. Virol.
79: 12455-12463
[Abstract]
[Full Text]
-
Dave, R. S., Pomerantz, R. J.
(2004). Antiviral Effects of Human Immunodeficiency Virus Type 1-Specific Small Interfering RNAs against Targets Conserved in Select Neurotropic Viral Strains. J. Virol.
78: 13687-13696
[Abstract]
[Full Text]
-
Day, J. R., Munk, C., Guatelli, J. C.
(2004). The Membrane-Proximal Tyrosine-Based Sorting Signal of Human Immunodeficiency Virus Type 1 gp41 Is Required for Optimal Viral Infectivity. J. Virol.
78: 1069-1079
[Abstract]
[Full Text]
-
Fujita, M., Sakurai, A., Yoshida, A., Miyaura, M., Koyama, A. H., Sakai, K., Adachi, A.
(2002). Amino Acid Residues 88 and 89 in the Central Hydrophilic Region of Human Immunodeficiency Virus Type 1 Vif Are Critical for Viral Infectivity by Enhancing the Steady-State Expression of Vif. J. Virol.
77: 1626-1632
[Abstract]
[Full Text]
-
Serhan, F., Jourdan, N., Saleun, S., Moullier, P., Duisit, G.
(2002). Characterization of Producer Cell-Dependent Restriction of Murine Leukemia Virus Replication. J. Virol.
76: 6609-6617
[Abstract]
[Full Text]
-
Lee, S.-F., Ko, C.-Y., Wang, C.-T., Chen, S. S.-L.
(2002). Effect of Point Mutations in the N Terminus of the Lentivirus Lytic Peptide-1 Sequence of Human Immunodeficiency Virus Type 1 Transmembrane Protein gp41 on Env Stability. J. Biol. Chem.
277: 15363-15375
[Abstract]
[Full Text]
-
Evans, D. T., Tillman, K. C., Desrosiers, R. C.
(2002). Envelope Glycoprotein Cytoplasmic Domains from Diverse Lentiviruses Interact with the Prenylated Rab Acceptor. J. Virol.
76: 327-337
[Abstract]
[Full Text]
-
Chen, B. K., Rousso, I., Shim, S., Kim, P. S.
(2001). Efficient assembly of an HIV-1/MLV Gag-chimeric virus in murine cells. Proc. Natl. Acad. Sci. USA
10.1073/pnas.261563198v1
[Abstract]
[Full Text]
-
Fujita, M., Yoshida, A., Miyaura, M., Sakurai, A., Akari, H., Koyama, A. H., Adachi, A.
(2001). Cyclophilin A-Independent Replication of a Human Immunodeficiency Virus Type 1 Isolate Carrying a Small Portion of the Simian Immunodeficiency Virus SIVMAC gag Capsid Region. J. Virol.
75: 10527-10531
[Abstract]
[Full Text]
-
West, J. T., Johnston, P. B., Dubay, S. R., Hunter, E.
(2001). Mutations within the Putative Membrane-Spanning Domain of the Simian Immunodeficiency Virus Transmembrane Glycoprotein Define the Minimal Requirements for Fusion, Incorporation, and Infectivity. J. Virol.
75: 9601-9612
[Abstract]
[Full Text]
-
Chen, S. S.-L., Lee, S.-F., Wang, C.-T.
(2001). Cellular Membrane-Binding Ability of the C-Terminal Cytoplasmic Domain of Human Immunodeficiency Virus Type 1 Envelope Transmembrane Protein gp41. J. Virol.
75: 9925-9938
[Abstract]
[Full Text]
-
Miller, E. D., Duus, K. M., Townsend, M., Yi, Y., Collman, R., Reitz, M., Su, L.
(2001). Human Immunodeficiency Virus Type 1 IIIB Selected for Replication In Vivo Exhibits Increased Envelope Glycoproteins in Virions without Alteration in Coreceptor Usage: Separation of In Vivo Replication from Macrophage Tropism. J. Virol.
75: 8498-8506
[Abstract]
[Full Text]
-
Zhu, P., Olson, W. C., Roux, K. H.
(2001). Structural Flexibility and Functional Valence of CD4-IgG2 (PRO 542): Potential for Cross-Linking Human Immunodeficiency Virus Type 1 Envelope Spikes. J. Virol.
75: 6682-6686
[Abstract]
[Full Text]
-
Chen, B. K., Rousso, I., Shim, S., Kim, P. S.
(2001). Efficient assembly of an HIV-1/MLV Gag-chimeric virus in murine cells. Proc. Natl. Acad. Sci. USA
98: 15239-15244
[Abstract]
[Full Text]
Top
Abstract
Text
