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J Biol Chem, Vol. 274, Issue 15, 9930-9936, April 9, 1999
From the Using a set of parental and recombinant murine
hepatitis virus strains, we demonstrate that the nucleocapsid protein
induces transcription of the novel fgl2 prothrombinase gene
and elevated procoagulant activity in those strains that produce
fulminant hepatitis. Chinese hamster ovary cells cotransfected with a
construct expressing nucleocapsid protein from susceptible strains and
with a luciferase reporter construct containing the fgl2
promoter showed a 6-fold increase in luciferase activity compared with
nontransfected cells or cells cotransfected with a construct expressing
nucleocapsid protein from resistant strains. Two deletions found at
coding sites 111-123 and 1143-1145 of structural domains I and III,
respectively, of the nucleocapsid gene may account for the differences
between pathogenic and nonpathogenic strains. Preliminary mapping of
the fgl2 promoter has defined a region from Murine coronavirus infection is recognized as one of the best
models for studying acute and chronic hepatitis of humans.
MHV1-3 infection in BALB/cJ
mice causes fulminant hepatic failure, which is characterized by
macrophage activation and marked production of proinflammatory
mediators. Especially intriguing is the ability of MHV-3 to induce
de novo synthesis of a unique procoagulant, the
fgl2 prothrombinase, encoded by the fgl2 gene
located on mouse chromosome 5 (1, 2). Several lines of evidence
implicate expression of this gene product in the pathogenesis of
fulminant murine hepatitis. First, levels of this prothrombinase
activity correlate with the severity of the disease (3, 4). Second, treatment of mice with a neutralizing monoclonal antibody to the MHV-3-induced prothrombinase prevents the lethality associated with
MHV-3 infection (5). Concordant with these observations, expression of
fgl2 prothrombinase in liver accounts for widespread fibrin
deposition in hepatic blood vessels and hepatocellular necrosis
(6).
The MHV genome is a single-stranded nonsegmented RNA of approximately
32 kb (7). The RNA genome contains seven or eight genes encoding three
or four structural proteins and four nonstructural proteins (8). An
important aspect of MHV biology is the high frequency of RNA-RNA
recombination between strains of MHV (9-11). RNA recombination may
contribute to viral pathogenesis and also provides a useful tool for
the study of genetic control of the biologic properties of viruses.
Studies using recombinant viruses derived from MHV-JHM and MHV-A59 have
demonstrated that the 3'-portion (about 25%) of the viral genome,
representing RNA genomic regions encoding for all of the structural
proteins, controls biologic properties such as organotropism of the
virus, the pattern of the virus-induced central nervous system
pathology in mice, plaque morphology, and virus yield in tissue culture
(12, 13). In this paper, we have defined the genetic basis for
induction of fgl2 gene transcription by MHV-3.
Mice
Female BALB/cJ mice, 6-8 weeks of age, from Charles River
Laboratories (St. Constant, Quebec) were kept in microisolated cages, housed in the animal facilities at the Toronto Hospital, and fed a
standard laboratory chow diet and water ad libitum.
Virus
MHV-3 was obtained from American Type Culture Collection (ATCC),
Rockville, MD) and plaque purified on monolayers of DBT cells. Parental
viruses A59, JHM, MHV-2, and two sets of recombinant viruses have been
described previously (14). The schematic representations of
oligonucleotide maps of the recombinant viruses are presented in Fig.
1. To ensure that the recombinant virus
strains are clonal, ML3 and ML11 were plaque purified three times in
17Cl-1 cells. The purified strains were used for creating nucleocapsid
(N) gene expression constructs and transfection experiments.
Cells
Peritoneal macrophages were harvested from BALB/cJ mice 4 days
after intraperitoneal administration of 1.5 ml of 3% thioglycolate (Difco Laboratories) as described previously (6). Macrophages were
resuspended in RPMI 1640 (ICN Biomedicals Inc., Costa Mesa, CA)
supplemented with 2 mM glutamine (Sigma) and 2%
heat-inactivated fetal calf serum (Flow Laboratories, Mississauga,
Ontario, Canada). Macrophages were greater than 95% in purity as
determined by morphology and nonspecific esterase stain. Viability
exceeded 95% by trypan blue exclusion. Chinese hamster ovary cell
line (CHO cells) were from ATCC.
Procoagulant Activity (PCA)
MHV and recombinant virus-infected macrophages, at a
multiplicity of infection of 2.5, were incubated for 8 h in RPMI
1640 supplemented with 2% fetal bovine serum and 200 mM
glutamine. Mock-infected macrophages and MHV-3-infected macrophages
represented negative and positive controls, respectively. Macrophages
were evaluated for functional PCA in a one-stage clotting assay, as described previously (15). After incubation, samples to be assayed for
PCA were washed three times with unsupplemented RPMI 1640 and
resuspended at a concentration of 106/ml. Samples were
assayed for the ability to shorten the spontaneous clotting time of
normal citrated human platelet-poor plasma. Milliunits of PCA were
assigned by reference to a standard curve generated with serial log
dilutions of a standard rabbit brain thromboplastin (Dade Division,
American Hospital Supply Co., Miami, FL).
RT-PCR
Expression of fgl2 was detected by RT-PCR. Freshly
isolated macrophages, at a multiplicity of infection of 2.5, were
infected with different strains of viruses for 6 h. 1 × 107 macrophages were pelleted in 1.5-ml Eppendorf tubes,
and total cellular RNA was isolated by 8 M acid-guanidium
hydrochloride extraction in a modified procedure as described
previously (16). The quantity and quality of RNA were examined by
spectrophotometry and on a 1% analytical agarose gel containing
formaldehyde. RNA (5 µg) was reverse transcribed using Moloney murine
leukemia virus reverse transcriptase in 20-µl reactions, as
recommended by the manufacturer. PCR was then performed in 50-µl
reactions using 1-µl portions of cDNA and the primers
fgl2 Creation of N Gene and fgl2 Promoter Constructs
Restriction enzymes used to create constructs were obtained from
Life Technologies, Inc. All plasmids were purified using Qiagen
Maxiprep Kits and grown in DH5 Escherichia coli bacteria (Life Technologies, Inc.).
N Gene Expression Constructs--
The entire N gene coding
regions and 3'-untranslated regions of MHV-A59, MHV-2, ML3, and ML11
were amplified by RT-PCR. RNA was originally extracted from infected
macrophages. The sense primer ACG ATG TCT TTT GTT CCT GGG was
phosphorylated chemically at position 1 to achieve directed insertion
and ligation of PCR products to its vector; the antisense primer at
position 1654 TTT TTT TTT GTG ATT CTT CCA had a poly(T) group to match
the poly(A) tail at the 3'-end of nucleocapsid genomic RNA. The N gene
fragments were subcloned into the 5.0-kb expression vector pCR3.1
(Invitrogen), under the control of the cytomegalovirus promoter and
bovine growth hormone 3'-processing signals. External restriction
endonuclease HindIII and PstI and internal
restriction endonuclease EcoRI, EcoRV were used
to analysis the size and orientation of N gene insert in recombinant
plasmid constructs.
Luciferase Reporter Constructs--
A 1.3-kb DNA fragment
flanking the 5'-end of mouse fgl2 was released by
restriction digestion with EcoRV and SalI from a
subclone pBluescript-m166 (pm166) of mouse genomic P1 plasmid (Genome
System Inc.) which contains the entire mouse fgl2 gene. This
fragment was sequenced by cycle sequencing on an automated DNA
sequencer (model 377, Applied Biosystems) using dideoxy dye terminator
chemistry. This sequence has been deposited into GenBank with the
Accession number AF025817 (Fig. 2) (17).
This 1.3-kb fragment was inserted into SmaI and
XhoI sites of the pGL2-basic luciferase reporter vector
(Promega) to form pfgl2(
The Nucleocapsid Protein of Murine Hepatitis Virus Type 3 Induces Transcription of the Novel fgl2 Prothrombinase
Gene*
,,,,,
,,,, and**
Multi-Organ Transplant Program and
Departments of Medicine and Pathology, Toronto Hospital, St. Michael's
Hospital, and the University of Toronto, Toronto, Ontario M5G 2C4,
Canada, the § Department of Molecular Microbiology and
Immunology and the Howard Hughes Medical Institute, University of
Southern California School of Medicine, Los Angeles, California 90033, and the Department of Pathology, Texas A & M University,
College Station, Texas 77843
ABSTRACT
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INTRODUCTION
EXPERIMENTAL PROCEDURES
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DISCUSSION
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372 to 306
upstream from the ATG translation initiation site to be responsive to
nucleocapsid protein. Hence, mapping of genetic determinants in
parental and recombinant strains demonstrates that the nucleocapsid
protein of strains that induce fulminant hepatitis is responsible for transcription of the fgl2 prothrombinase gene. These
studies provide new insights into the role of the nucleocapsid gene in
the pathogenesis of viral hepatitis.
INTRODUCTION
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ABSTRACT
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EXPERIMENTAL PROCEDURES
RESULTS
DISCUSSION
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EXPERIMENTAL PROCEDURES
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ABSTRACT
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EXPERIMENTAL PROCEDURES
RESULTS
DISCUSSION
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View larger version (29K):
[in a new window]
Fig. 1.
Schematic representation of oligonucleotide
maps of the recombinant viruses (MHV-A59 × JHM)
and (MHV-A59 × MHV-2). L, leader
sequence; Pol, RNA-dependent RNA polymerase
gene; HN, hemagglutinin-esterase glycoprotein gene;
S, spike protein; M, matrix glycoprotein gene;
N, nucleocapsid protein gene. The data are from Ref.
22.
318 (TGC CCA CGC TGA CCA TCC A) corresponding to
nucleotides 318-336 of BALB/cJ fgl2 cDNA (M 15761) and
fgl2 1224 (GAG ACA ACG ATC GGT ACC CCT) corresponding to
nucleotides 1224-1244 of BALB/cJ fgl2 cDNA. (M16238),
which yield a 906-base pair band in 1% agarose DNA gel. Amplification products were not obtained when reverse transcriptase was omitted (data
not shown). RT-PCR for glyceraldehyde-3-phosphate dehydrogenase was
also set up as an internal control to assess the quality of first
strand synthesis.
1328)LUC. 5'-Deletion constructs of
fgl2 promoter were made by first amplifying the specific
fragment using pm166 as template and then cloned into pCR2.1 cloning
vector (Strategene) and resubcloned into pGL2-basic plasmid at
XhoI and HindIII sites. The reverse primer (GCC
ACA ACC AAC CAG GAA G) was used to make all deletion constructs by PCR
amplification. The upstream primers used were: GAG CTG AGT GAT GGG GAA
GGA for pfgl2(693)LUC, CCA CTG ACG ATT ACA TAG CC for
pfgl2(625)LUC, GGA CCT TTG TTC TGA TTA GGG GC for
pfgl2(511)LUC, CGC AGA CAT TTA GAC GTT CC for pfgl2(372)LUC, and
GGG CAC TGG TAT TAC AAC TGT for pfgl2(306)LUC. All
promoter-luciferase report constructs were sequenced to confirm the
orientation and to verify the sequence. Positive control, pGL2 control
plasmid with SV40 promoter, and Rous sarcoma virus
-galactosidase vector were from Promega. A 2-kb tissue factor
promoter construct pTF(2kb)LUC was a kind gift of Dr. Nigel Mackman
(18).
View larger version (80K):
[in a new window]
Fig. 2.
Schematic diagram of the organization of the
fgl2 gene is shown in the upper panel. The
lower panel shows the sequence of the 1.3-kb DNA-flanking
5'-end of fgl2. The sequence shows the overlapping 400 base
pairs at the 3'-end of this fragment and the 5'-end of the published
sequence by Koyama et al. (17) with the accession number
M15761 are consistent. The putative cis-elements responsive
to N protein and initiating ATG for translation are indicated in
bold and underlined.
N Gene Sequence of Different Virus Strains
The N gene sequence of multiple clones for each strain of virus was determined using primer-directed strategies by cycle sequencing on an automated DNA sequencer, using the Applied Biosystems PRISMTM dRhodamine Terminator Cycle Sequencing Reading Reaction kit (model 377, PE Applied Biosystems). The T7 primer and pCR3.1 reverse primer were used for 5' to 3' and 3' to 5' sequence, respectively. A new primer CTC AGG GCT TTT ATG TTG AAG (MHV-ND557) at position 557 was also designed based on the outcome of sequencing and the published cDNA sequence of MHV-A59 to complete the sequencing. Extension products were purified by ethanol/sodium acetate precipitation. Samples were subjected to electrophoresis on the PRISM 310. The sequence was analyzed using the DNAsis for windows, sequence analysis software (Hitachi Software Engineering America Ltd., San Bruno, CA).
Transfection
CHO cells were cultured in six-well plates until 50-80%
confluence. 1 µg of N gene construct DNA or 1 µg of empty pCR3.1
vector, 0.5 µg of fgl2 promoter-luciferase report
construct DNA, and 0.25 µg of -galactosidase DNA (as a marker for
transfection efficiency by -galactosidase assay) in 100 µl of
Opti-DMEM were mixed by vortexing with 3.5 µl of
LipofectAMINETM (2 µg/µl) in 100 µl of Opti-DMEM
medium. After incubation of the mixture at room temperature for 30 min,
1.8 ml of Opti-DMEM medium was added to bring up the volume to 2 ml. 1 ml of this mixture was distributed into one of the duplicated wells
with CHO cells, and transfection were performed at 37 °C with 5%
CO2 for 44-48 h. Cells were harvested in lysis buffer and
freeze-thawed three times in liquid N2. Aliquots of
supernatants were assayed for -galactosidase and luciferase activity.
Western Blot
At 48 h post-transfection with N gene and
pfgl2(1328)LUC, cultures of 1 × 106 CHO cells were
collected and lysed in 100 µl of Western blot lysis buffer with
protease inhibitor. 20 µl of lysate was resolved by
SDS-polyacrylamide gel electrophoresis and then transferred to a
nitrocellulose membrane. After blocking in 4% milk and
phosphate-buffered saline for 1 h, membrane was probed with a
monoclonal antibody against the N protein at 4 °C overnight followed
by washing a total of five times in 2% milk, phosphate-buffered
saline, and Tween. The membrane was then incubated with goat anti-mouse
IgG labeled with horseradish peroxidase for 1 h and washed five
times in 2% milk, phosphate-buffered saline, and Tween. Substrates
luminol and Enhancer were added and incubated for 1 min. The membrane was then exposed to Kodak XAR-5 film with intensifying screens for 10 min.
Statistical Analysis
Data are expressed as mean ± S.D. where applicable.
Student's t test for unpaired samples (two-tailed) was used
to analyze the data.
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Expression of BALB/cJ Macrophage Functional PCA Induced by
Parental Viruses and Their Recombinants--
Studies were undertaken
using parental A59, JHM, and MHV-2 strains and two sets of recombinant
viruses between them (A59 × JHM, A59 × MHV-2) (Fig. 1).
MHV-A59 infection of macrophages resulted in a marked elevation of
functional PCA, similar to what was reported previously for MHV-3 (1,
6), whereas JHM and MHV-2 failed to induce PCA (Fig.
3A). A59 × JHM-derived
recombinants B1, RL1, and IL27, in which the 3'-portion of the genome
is derived from MHV-A59, induced high level of functional PCA. In
contrast, CA13 and CA43, two recombinants in which the 3'-portion of
the genome is derived from MHV-JHM, did not induce PCA, suggesting that
the 3'-portion of the MHV-A59 genome may contain a viral genetic
determinant needed for induction of functional PCA, which is lacking in
the corresponding region of MHV-JHM. To delineate better the candidate genes required for induction of fgl2, we next studied a set
of recombinants derived from MHV-A59 × MHV-2, which have multiple crossovers in a single genome, particularly within the 3'-portion of
the genome. Recombinants ML3 and ML10 induced functional PCA, whereas
ML11 did not (Fig. 3B). The differences between recombinants ML3 and ML11 in the 3'-portion of the genome maps within the 5'-end of
the N gene. Therefore, the ability of recombinants to induce functional
PCA parallels the presence or absence of MHV-A59 sequences representing
the N gene, strongly suggesting that the MHV-A59 N gene is responsible
for activation of fgl2.
|
Induction of fgl2 Transcription by Parental and Recombinant
Viruses--
RT-PCR analysis demonstrated that the presence or absence
of detectable fgl2 mRNA in macrophages infected with
various parental or recombinant viruses correlated with the results of
assays for functional fgl2 prothrombinase (Fig.
4).
|
Sequence Comparison of N Genes--
The entire N gene sequence was
determined for MHV-A59, MHV-2, and the recombinant viruses ML3 and
ML11, as described under "Experimental Procedures" (sequence data
not shown). A comparison of different N gene sequences is shown in
Table I. Compared with the published
sequence of A59 in GenBank (M35156), the sequence of MHV-A59 used in
this study had two point mutations at nucleotides 441 (T 
A) and
1613 (T C); ML3 had three point mutations at nucleotides 405 (C A), 441 (T A), and 1613 (T C). Sequence differences between the
N genes of MHV-A59 and MHV-2 (AF061835) were mainly within two regions
corresponding to nucleotides 400-500 and 1100-1200 of the MHV-A59
sequence. In addition, MHV-2 had a 12-nucleotide deletion at 111-123
and a 3-nucleotide insertion at 1143-1145 compared with MHV-A59. In
contrast, the 3'-untranslated regions following the N gene
are completely identical between MHV-A59 and MHV-2.
|
Effect of N Protein on fgl2 Promoter Activity--
To establish
that the N gene of MHV is responsible for the induction of the
fgl2 gene, cotransfection of CHO cells with the N gene under
the cytomegalovirus promoter and fgl2('1328)LUC were performed. The
expression of the N protein was confirmed by Western blotting (Fig.
5). CHO cells cotransfected with the N
gene construct from A59 and a murine pfgl2('1328)LUC showed a 6-fold
increase in luciferase activity compared with cells cotransfected with the pCR 3.1 empty vector (Fig. 6). In
contrast, MHV-2 N protein expression did not enhance fgl2
expression. To confirm the specificity of the effect of N protein on
fgl2 promoter activity, pTF(2kb)LUC and a pGL2-control
vector under SV40 promoter were each cotransfected with the MHV-A59 N
gene construct. There was no significant increase in luciferase
expression when these two constructs were cotransfected with or without
the MHV-A59 N gene construct (Fig. 6).
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Mapping of the fgl2 Promoter--
To characterize the region in
the fgl2 promoter which is responsive to N protein of
MHV-A59, constructs containing progressive deletions of the 1328 base
pair fragment were cotransfected with either N gene constructs or empty
pCR3.1 vector in CHO cells (Fig. 7A). Preliminary mapping of
the fgl2 promoter has defined a region from 372 to 306
to be responsive to induction of N protein. The activity of the
deletion construct 306 was comparable to the promoterless plasmid
pGL2-basic. Using DNAsis software, three positive cis-acting
regulatory elements were identified within this region which included a
liver factor A1 binding element (LF-A1, 332 to 325), human
cytomegalovirus immediate-early gene 1.2 (IE1.2, 345 to 336)
regulatory elements, and granulocyte macrophage colony-stimulating
factor binding element (GMCSF, 353 to 346) (Fig.
7B).
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Studies using a model of viral hepatitis induced by infection with MHV-3 have provided significant insight into the mechanisms underlying the pathogenesis of this disease and have suggested novel approaches to therapy (2, 19, 20). Furthermore, recent studies have demonstrated the role of the selective expression of the fgl2 prothrombinase in the pathogenesis of MHV-3-induced fulminant liver failure (1, 2, 5, 6).
The studies presented here demonstrate that infection of macrophages with MHV-A59 resulted in transcription of fgl2 and elevated functional prothrombinase activity, a result similar to that observed during infection of macrophages with MHV-3. This contrasts with the results obtained with MHV-JHM and MHV-2, which do not induce elevations of prothrombinase in infected macrophages. Recombinant viruses (n = 5) which derive a portion of their genomic RNA from the 3'-region of MHV-A59 induce functional prothrombinase, whereas those containing a 3'-region derived from JHM or MHV-2 (n = 5) do not, suggesting that the 3'-portion of the genome may play an important role in the induction of fgl2 transcription. The sequence differences in the genome in the 3'-area of interest lie mainly within the 5'-end of the N gene. The sequence differences in the N gene between inducers and noninducers are a 12-nucleotide deletion at nucleotides 111-123 of the coding region for the structural domain I and a 3-nucleotide insertion at 1143-1145 of the coding region for structural domain III, which may account for the inability of JHM or MHV-2 to induce fgl2. CHO cells cotransfected with the N gene construct from A59 and with the fgl2 promoter construct showed a 6-fold increase in luciferase activity in contrast to base-line or MHV-2-cotransfected cells.
These findings strongly suggest that the N protein is responsible for fgl2 induction. It should be noted that induction of fgl2 could not be explained by differences in virus replication, as MHV-2, a noninducer, replicates to higher titers than A59, whereas A59 replicates to higher titers than JHM. It is also of great interest that all of the recombinants of MHV-2 × A59 have the MHV-2-derived leader sequence, whereas the majority of recombinants between A59 × JHM contain the A59 leader (21). It is not clear whether the leader sequence differences among viruses are responsible for the altered growth property of the virus.
MHV N protein has been proposed to consists of three conserved structural domains (I basic, II basic, and III acidic) which are tethered to each other by two regions of variable amino acid composition (designated A and B) (22). The sequence differences in the N gene between A59 and MHV-2 lie within two regions corresponding to domain I (nucleotides 400-500) and domain III (nucleotides 1100-1200), respectively. These differences may account for the inability of MHV-2 to induce the fgl2 gene.
Cotransfection of an N gene expression construct with the fgl2 promoter/reporter luciferase construct in the CHO cell line confirms that the N gene of A59 accounts for induction of fgl2. To confirm the specificity of the induction of N protein for the fgl2 promoter, the same experiment was performed with two irrelevant constructs. Neither showed enhancement of luciferase activity when cotransfected with fgl2 promoter construct. However, this does not suggest that the N protein will not induce the expression of other proinflammatory genes, which are important in the pathogenesis of MHV-3-induced hepatitis (23). Possible mechanisms by which N protein induces fgl2 prothrombinase expression include the transport of the N protein into the nucleus of infected cells, acting as a transcription activator for fgl2, or modulation of signal transduction pathways that regulate host transcription machinery, or production of additional transcription factors thereby increasing the steady-state levels for fgl2 transcripts. Recent work by both nuclear runoff assays and transient transfection experiments have demonstrated that the induction of fgl2 mRNA by MHV-3 infection is at least in part attributable to new transcription (18). An alternative mechanism may be N protein binding directly to fgl2 mRNA, thus altering the rate of fgl2 transcript degradation. Further experiments are now in progress to clarify the mechanisms involved.
Preliminary mapping of the fgl2 promoter has defined a
region from 372 to 306 to be responsive to the N protein. At
present, we have not determined the precise cis-element(s)
that are necessary for transcription. However, we have identified three
putative cis-elements. Of particular interest, previous
reports have suggested that LF-A1 was typical of a liver-specific gene
and liver-enriched transcription factor. Furthermore, LF-A1 is known to
regulate gene expression of coagulation factors IX, X, and XII
(24-26). Additionally, granulocyte macrophage colony-stimulating
factor is released by activated T lymphocytes, monocytes, endothelial cells, and fibroblasts treated with proinflammatory cytokines (27, 28).
IE1.2 has been implicated as human cytomegalovirus immediate-early gene
1 and 2 regulatory elements, providing a link between virus infection
and inflammation (29). These data do not exclude the presence of other
cis-elements that might contribute to transcription of
fgl2, and studies now ongoing will firmly define relevant
elements necessary for fgl2 transcription.
Recent studies have shown that the severity of hepatic injury in patients with hepatitis B is related to the synthesis and expression of nucleocapsid protein of the hepatitis B virus, suggesting that the accumulation of hepatitis B core antigen may damage hepatocytes directly or may serve to stimulate cell-mediated immune responses (30, 31). We have recently cloned and sequenced the human prothrombinase gene (hfgl2) gene and have shown its expression in the liver of three patients with fulminant hepatic failure.2 Studies are now in progress to determine if hepatitis B core antigen induces transcription of hfgl2.
In conclusion, mapping of genetic determinants in parental and
recombinant MHV strains demonstrates that the N protein of strains of
MHV which induce fulminant hepatic favor is responsible for enhanced
transcription of the fgl2 prothrombinase gene. These studies
may provide significant insights into the viral pathogenesis of human
diseases such as hepatitis B and C in which core antigen (nucleocapsid
protein) influences disease activity.
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ACKNOWLEDGEMENTS |
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We thank Charmaine Beal and Dawn Paluch for technical assistance.
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FOOTNOTES |
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* This work was supported by Medical Research Council of Canada Grant GR13298 and National Institutes of Health Grants AI31069, AI19244, and NS18146.
The nucleotide sequence(s) reported in this paper has been submitted to the GenBankTM/EMBL Data Bank with accession number(s) AF025817.
¶ Investigator of the Howard Hughes Medical Institute.
** To whom correspondence should be addressed: Multi-Organ Transplant Program, The Toronto Hospital, 621 University Avenue, 10th floor, Rm. 151, Toronto, Ontario, Canada M5G 2C4. Tel.: 416-340-5166; Fax: 416-340-3378; E-mail: fgl2{at}msn.com.
2 Q. Ning, M. Liu, P. Kongkham, M. M. C. Lai, P. A. Marsden, J. Tseng, B. Pereira, M. Belyavskyi, J. Leibowitz, M. J. Phillips, and G. Levy, manuscript in preparation.
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ABBREVIATIONS |
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The abbreviations used are: MHV, murine hepatitis virus; kb, kilobase(s); N, nucleocapsid; CHO, Chinese hamster ovary; PCA, procoagulant activity; RT, reverse transcription; PCR, polymerase chain reaction; LUC, luciferase; DMEM, Dulbecco's modified Eagle's medium.
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