bluuebunny/crossref_metadata_2025_split huggingface dataset:
Duck Hepatitis B Virus Expresses a Regulatory HBx-Like Protein from a Hidden Open Reading Frame
Authors: Chang Shau-Feng , Netter Hans Jürgen , Hildt Eberhard , Schuster Ralph , Schaefer Stephan , Hsu Yin-Chen , Rang Andreas , Will Hans 
Published: July 2002

ABSTRACTDuck hepatitis B viruses (DHBV), unlike mammalian hepadnaviruses, are thought to lack X genes, which encode transcription-regulatory proteins believed to contribute to the development of hepatocellular carcinoma. A lack of association of chronic DHBV infection with hepatocellular carcinoma development supports this belief. Here, we demonstrate that DHBV genomes have a hidden open reading frame from which a transcription-regulatory protein, designated DHBx, is expressed both in vitro and in vivo. We show that DHBx enhances neither viral protein expression, intracellular DNA synthesis, nor virion production when assayed in the full-length genome context in LMH cells. However, similar to mammalian hepadnavirus X proteins, DHBx activates cellular and viral promoters via the Raf–mitogen-activated protein kinase signaling pathway and localizes primarily in the cytoplasm. The functional similarities as well as the weak sequence homologies of DHBx and the X proteins of mammalian hepadnaviruses strongly suggest a common ancestry of ortho- and avihepadnavirus X genes. In addition, our data disclose similar intracellular localization and transcription regulatory functions of the corresponding proteins, raise new questions as to their presumed role in hepatocarcinogenesis, and imply unique opportunities for deciphering of their still-enigmatic in vivo functions.
Use of Intron-Disrupted Polyadenylation Sites To Enhance Expression and Safety of Retroviral Vectors
Authors: Ismail Said I. , Rohll Jonathan B. , Kingsman Susan M. , Kingsman Alan J. , Uden Mark 
Published: July 2002

ABSTRACT
Normal mRNA polyadenylation signals are composed of an AAUAAA motif and G/U box spaced 20 to 30 bp apart. If this spacing is increased further, then polyadenylation is disrupted. Previously it has been demonstrated that insertion of an intron will similarly disrupt this signal even though such introns are removed during a nuclear splicing reaction (X. Liu and J. Mertz, Nucleic Acids Res. 21:5256–5263, 1993). This observation has led to the suggestion that polyadenylation site selection is undertaken prior to intron excision. We now present results that both support and extend these observations and in doing so create a novel class of retroviral expression vector with improved qualities. We found that when an intron-disrupted polyadenylation signal is inserted within a retroviral expression vector, such a signal, although reformed in the producer cell, remains benign until transduction, where it is then preferentially used. Thus, we demonstrate that upon transduction these vectors now produce a majority of shortened subgenomic species and as a consequence have a reduced tendency for subsequent mobilization from transduced cells. In addition, we demonstrate that the use of this internal signal leads to enhanced expression from such vectors and that this is achieved without any loss in titer. Therefore, split polyadenylation signals confer enhanced performance and improved safety upon retroviral expression vectors into which they are inserted. Such split signals may prove useful for the future optimization of retroviral vectors in gene therapy.
Kinetics of Hepadnavirus Loss from the Liver during Inhibition of Viral DNA Synthesis
Authors: Zhu Yuao , Yamamoto Toshiki , Cullen John , Saputelli Jeffry , Aldrich Carol E. , Miller Darren S. , Litwin Samuel , Furman Phillip A. , Jilbert Allison R. , Mason William S. 
Published: July 2002

ABSTRACT

Hepadnaviruses replicate by reverse transcription, which takes place in the cytoplasm of the infected hepatocyte. Viral RNAs, including the pregenome, are transcribed from a covalently closed circular (ccc) viral DNA that is found in the nucleus. Inhibitors of the viral reverse transcriptase can block new DNA synthesis but have no direct effect on the up to 50 or more copies of cccDNA that maintain the infected state. Thus, during antiviral therapy, the rates of loss of cccDNA, infected hepatocytes (1 or more molecules of cccDNA), and replicating DNAs may be quite different. In the present study, we asked how these losses compared when woodchucks chronically infected with woodchuck hepatitis virus were treated with L-FMAU [1-(2-fluoro-5-methyl-β-
l
-arabinofuranosyl) uracil], an inhibitor of viral DNA synthesis. Viremia was suppressed for at least 8 months, after which drug-resistant virus began replicating to high titers. In addition, replicating viral DNAs were virtually absent from the liver after 6 weeks of treatment. In contrast, cccDNA declined more slowly, consistent with a half-life of ∼33 to 50 days. The loss of cccDNA was comparable to that expected from the estimated death rate of hepatocytes in these woodchucks, suggesting that death of infected cells was one of the major routes for elimination of cccDNA. However, the decline in the actual number of infected hepatocytes lagged behind the decline in cccDNA, so that the average cccDNA copy number in infected cells dropped during the early phase of therapy. This observation was consistent with the possibility that some fraction of cccDNA was distributed to daughter cells in those infected hepatocytes that passed through mitosis.
Tissue Distribution and Timing of Appearance of Polytropic Envelope Recombinants during Infection with SL3-3 Murine Leukemia Virus or Its Weakly Pathogenic SL3ΔMyb5 Mutant
Authors: Rulli Karen , Lobelle-Rich Patricia A. , Trubetskoy Alla , Lenz Jack , Levy Laura S. 
Published: July 2002

ABSTRACT
A time course analysis was performed to identify the sites of formation and timing of appearance of polytropic recombinant viruses following infection of NIH/Swiss mice with the murine retrovirus SL3-3 murine leukemia virus (SL3) or with a weakly pathogenic mutant termed SL3ΔMyb5. The results indicated that (i) polytropic recombinant viruses occur initially in the thymus of SL3-infected animals, (ii) the timing of appearance of polytropic recombinants in bone marrow is not consistent with their participation in the previously reported formation of transplantable tumor-forming cells at 3 to 4 week postinoculation, and (iii) the efficient generation of recombinant virus is correlated with efficient tumor induction.
Amino Acids of Epstein-Barr Virus Nuclear Antigen 3A Essential for Repression of Jκ-Mediated Transcription and Their Evolutionary Conservation
Authors: Dalbiès-Tran Rozenn , Stigger-Rosser Evelyn , Dotson Travis , Sample Clare E. 
Published: July 2002

ABSTRACT
Epstein-Barr virus (EBV) nuclear antigen 3A (EBNA-3A) is essential for virus-mediated immortalization of B lymphocytes in vitro and is believed to regulate transcription of cellular and/or viral genes. One known mechanism of regulation is through its interaction with the cellular transcription factor Jκ. This interaction downregulates transcription mediated by EBNA-2 and Jκ. To identify the amino acids that play a role in this interaction, we have generated mutant EBNA-3A proteins. A mutant EBNA-3A protein in which alanine residues were substituted for amino acids 199, 200, and 202 no longer downregulated transcription. Surprisingly, this mutant protein remained able to coimmunoprecipitate with Jκ. Using a reporter gene assay based on the recruitment of Jκ by various regions spanning EBNA-3A, we have shown that this mutation abolished binding of Jκ to the N-proximal region (amino acids 125 to 222) and that no other region of EBNA-3A alone was sufficient to mediate an association with Jκ. To determine the biological significance of the interaction of EBNA-3A with Jκ, we have studied its conservation in the simian lymphocryptovirus herpesvirus papio (HVP) by cloning HVP-3A, the homolog of EBNA-3A encoded by this virus. This 903-amino-acid protein exhibited 37% identity with its EBV counterpart, mainly within the amino-terminal half. HVP-3A also interacted with Jκ through a region located between amino acids 127 and 223 and also repressed transcription mediated through EBNA-2 and Jκ. The evolutionary conservation of this function, in proteins that have otherwise significantly diverged, argues strongly for an important biological role in virus-mediated immortalization of B lymphocytes.
Cell Cycle Analysis of Epstein-Barr Virus-Infected Cells following Treatment with Lytic Cycle-Inducing Agents
Authors: Rodriguez Antonio , Jung Eun Joo , Flemington Erik K. 
Published: July 2002

ABSTRACT

While Epstein-Barr virus (EBV) latency-associated gene expression is associated with cell cycle progression, the relationship between the EBV lytic program and the cell cycle is less clear. Using four different EBV lytic induction systems, we address the relationship between lytic cycle activation and the cell cycle. In three of these systems, G
0
or G
1
cell growth arrest signaling is observed prior to detection of the EBV immediate-early gene product Zta. In tetradecanoyl phorbol acetate-treated P3HR1 cultures and in 5-iodo-2′-deoxyuridine-treated NPC-KT cultures, cell cycle analysis of Zta-expressing cell populations showed a significant G
1
bias during the early stages of lytic cycle progression. In contrast, treatment of the cell line Akata with anti-immunoglobulin (Ig) results in rapid induction of immediate-early gene expression, and accordingly, activation of the immediate-early gene product Zta precedes significant anti-Ig-induced cell cycle effects. Nevertheless, cell cycle analysis of the Zta-expressing population following anti-Ig treatment shows a bias for cells in G
1
, indicating that anti-Ig-mediated induction of Zta occurs more efficiently in cells traversing G
1
. Last, although 5-azacytidine treatment of Rael cells results in a G
1
arrest in the total cell population which precedes the induction of Zta, cell cycle analysis of the Zta-expressing population shows a significant bias for cells with an apparent G
2
/M DNA content. This bias may result, in part, from activation of Zta expression following demethylation of the Zta promoter during S-phase. Together, these studies indicate that induction of Zta occurs through several distinct mechanisms, some of which may involve checkpoint signaling.
Efficient Conversion of Normal Prion Protein (PrP) by Abnormal Hamster PrP Is Determined by Homology at Amino Acid Residue 155
Authors: Priola Suzette A. , Chabry Joëlle , Chan Kaman 
Published: July 2002

ABSTRACT
In the transmissible spongiform encephalopathies, disease is closely associated with the conversion of the normal proteinase K-sensitive host prion protein (PrP-sen) to the abnormal proteinase K-resistant form (PrP-res). Amino acid sequence homology between PrP-res and PrP-sen is important in the formation of new PrP-res and thus in the efficient transmission of infectivity across species barriers. It was previously shown that the generation of mouse PrP-res was strongly influenced by homology between PrP-sen and PrP-res at amino acid residue 138, a residue located in a region of loop structure common to PrP molecules from many different species. In order to determine if homology at residue 138 also affected the formation of PrP-res in a different animal species, we assayed the ability of hamster PrP-res to convert a panel of recombinant PrP-sen molecules to protease-resistant PrP in a cell-free conversion system. Homology at amino acid residue 138 was not critical for the formation of protease-resistant hamster PrP. Rather, homology between PrP-sen and hamster PrP-res at amino acid residue 155 determined the efficiency of formation of a protease-resistant product induced by hamster PrP-res. Structurally, residue 155 resides in a turn at the end of the first alpha helix in hamster PrP-sen; this feature is not present in mouse PrP-sen. Thus, our data suggest that PrP-res molecules isolated from scrapie-infected brains of different animal species have different PrP-sen structural requirements for the efficient formation of protease-resistant PrP.
Visualization of Intracellular Movement of Vaccinia Virus Virions Containing a Green Fluorescent Protein-B5R Membrane Protein Chimera
Authors: Ward Brian M. , Moss Bernard 
Published: July 2002

ABSTRACT
We produced an infectious vaccinia virus that expressed the B5R envelope glycoprotein fused to the enhanced green fluorescent protein (GFP), allowing us to visualize intracellular virus movement in real time. Previous transfection studies indicated that fusion of GFP to the C-terminal cytoplasmic domain of B5R did not interfere with Golgi localization of the viral protein. To determine whether B5R-GFP was fully functional, we started with a B5R deletion mutant that made small plaques and inserted the B5R-GFP gene into the original B5R locus. The recombinant virus made normal-sized plaques and acquired the ability to form actin tails, indicating reversal of the mutant phenotype. Moreover, immunogold electron microscopy revealed that both intracellular enveloped virions (IEV) and extracellular enveloped virions contained B5R-GFP. By confocal microscopy of live infected cells, we visualized individual fluorescent particles, corresponding to IEV in size and shape, moving from a juxtanuclear location to the periphery of the cell, where they usually collected prior to association with actin tails. The fluorescent particles could be seen emanating from cells at the tips of microvilli. Using a digital camera attached to an inverted fluorescence microscope, we acquired images at 1 frame/s. At this resolution, IEV movement appeared saltatory; in some frames there was no net movement, whereas in others movement exceeded 2 μm/s. Further studies indicated that IEV movement was reversibly arrested by the microtubule-depolymerizing drug nocodazole. This result, together with the direction, speed, and saltatory motion of IEV, was consistent with a role for microtubules in intracellular transport of IEV.
Interferon Action against Human Parainfluenza Virus Type 3: Involvement of a Novel Antiviral Pathway in the Inhibition of Transcription
Authors: Choudhary Suresh , Gao Jing , Leaman Douglas W. , De Bishnu P. 
Published: July 2002

ABSTRACT
Interferon (IFN)-induced 2′-5′ oligoadenylate synthetase (2-5A synthetase)/RNase L, PKR, and Mx proteins are considered to be the principal antiviral protein pathways through which IFN induces an antiviral state. It was previously reported that human parainfluenza virus type 3 (HPIV3) multiplication was inhibited by IFN-α in human lung epithelial cells A549 and that MxA was found to contribute to the inhibition process (Zhao et al., Virology 220:330–338, 1996). Viral primary transcription was dramatically inhibited in A549 cells after IFN-α treatment, but a step following primary transcription was inhibited in U87-MxA cells constitutively expressing MxA. Here we have investigated the role of MxA, believed to be cell type specific, and other antiviral pathways in the inhibition of viral primary transcription. Our data indicate that a novel IFN-induced pathway(s) is involved in the inhibition of primary transcription. This is based on the following findings: (i) IFN-α inhibited viral primary transcription in U87-MxA and other cell types including cells lacking MxA; (ii) cells constitutively expressing 2-5A synthetase had no antiviral effect against HPIV3; and (iii) primary transcription occurred in the absence of protein synthesis, a step of PKR target. The novel antiviral pathway(s) was induced by both IFN-α and IFN-γ to establish an effective antiviral state against HPIV3. By using IFN-α-signaling mutant cells, we found that IFN-γ could elicit antiviral effect against HPIV3 without cross talk with the IFN-α-signaling pathway. These data provide the first evidence that a novel antiviral pathway(s) contributes to the antiviral action of IFN against a nonsegmented negative-strand RNA virus by targeting the primary transcription.
Construction of Avian Adenovirus CELO Recombinants in Cosmids
Authors: François Achille , Eterradossi Nicolas , Delmas Bernard , Payet Vincent , Langlois Patrick 
Published: July 2002

ABSTRACT
The avian adenovirus CELO is a promising vector for gene transfer applications. In order to study this potentiality, we developed an improved method for construction of adenovirus vectors in cosmids that was used to engineer the CELO genome. For all the recombinant viruses constructed by this method, the ability to produce infectious particles and the stability of the genome were evaluated in a chicken hepatocarcinoma cell line (LMH cell line). Our aim was to develop a replication-competent vector for vaccination of chickens, so we first generated knockout point mutations into 16 of the 22 unassigned CELO open reading frames (ORFs) to determine if they were essential for virus replication. As the 16 independent mutant viruses replicated in our cellular system, we constructed CELO genomes with various deletions in the regions of these nonessential ORFs. An expression cassette coding for the enhanced green fluorescent protein (eGFP) was inserted in place of these deletions to easily follow expression of the transgene and propagation of the vector in cell monolayers. Height-distinct GFP-expressing CELO vectors were produced that were all replication competent in our system. We then retained the vector backbone with the largest deletion (i.e., 3.6 kb) for the construction of vectors carrying cDNA encoding infectious bursal disease virus proteins. These CELO vectors could be useful for vaccination in the chicken species.
Biophysical Analysis of Natural Variants of the Multimerization Region of Epstein-Barr Virus Lytic-Switch Protein BZLF1
Authors: Hicks Matthew R. , Balesaria Sara , Medina-Palazon Cahora , Pandya Maya J. , Woolfson Derek N. , Sinclair Alison J. 
Published: July 2002

ABSTRACT
BZLF1 plays a key role in the induction of Epstein-Barr virus (EBV) replication. On the basis of limited sequence homology and mutagenesis experiments, BZLF1 has been described as a member of the bZip family of transcription factors, but this prospect has not been rigorously tested to date. Here, we present biophysical analysis of the multimerization domain of BZLF1, from three natural variants of EBV, and demonstrate for the first time that the region between amino acids 196 and 227 is sufficient to direct folding as a coiled-coil dimer in vitro.
Inhibition of L-Deleted Foot-and-Mouth Disease Virus Replication by Alpha/Beta Interferon Involves Double-Stranded RNA-Dependent Protein Kinase
Authors: Chinsangaram Jarasvech , Koster Marla , Grubman Marvin J. 
Published: July 2002

ABSTRACT

We previously demonstrated that the ability of foot-and-mouth disease virus (FMDV) to form plaques in cell culture is associated with the suppression of alpha/beta interferon (IFN-α/β). In the present study, we used
Escherichia coli
-expressed porcine and bovine IFN-α or -β individually to demonstrate that each was equally effective in inhibiting FMDV replication. The block in FMDV replication appeared to be at the level of protein translation, suggesting a role for double-stranded RNA-dependent protein kinase (PKR). In support of these findings, treatment of porcine and bovine cells with 2-aminopurine, an inhibitor of PKR, increased the yield of virus 8.8- and 11.2-fold, respectively, compared to that in untreated infected cells. In addition, results of FMDV infection in mouse embryonic fibroblast cells derived from gene knockout mice lacking the gene for RNase L
−/−
or PKR
−/−
or both indicated an important role for PKR in the inhibition of FMDV replication.
The Ability of an Oligomeric Human Immunodeficiency Virus Type 1 (HIV-1) Envelope Antigen To Elicit Neutralizing Antibodies against Primary HIV-1 Isolates Is Improved following Partial Deletion of the Second Hypervariable Region
Authors: Barnett S. W. , Lu S. , Srivastava I. , Cherpelis S. , Gettie A. , Blanchard J. , Wang S. , Mboudjeka I. , Leung L. , Lian Y. , Fong A. , Buckner C. , Ly A. , Hilt S. , Ulmer J. , Wild C. T. , Mascola J. R. , Stamatatos L. 
Published: July 2002

ABSTRACT
Partial deletion of the second hypervariable region from the envelope of the primary-like SF162 virus increases the exposure of certain neutralization epitopes and renders the virus, SF162ΔV2, highly susceptible to neutralization by clade B and non-clade B human immunodeficiency virus (HIV-positive) sera (L. Stamatatos and C. Cheng-Mayer, J. Virol. 78:7840–7845, 1998). This observation led us to propose that the modified, SF162ΔV2-derived envelope may elicit higher titers of cross-reactive neutralizing antibodies than the unmodified SF162-derived envelope. To test this hypothesis, we immunized rabbits and rhesus macaques with the gp140 form of these two envelopes. In rabbits, both immunogens elicited similar titers of binding antibodies but the modified immunogen was more effective in eliciting neutralizing antibodies, not only against the SF162ΔV2 and SF162 viruses but also against several heterologous primary HIV type 1 (HIV-1) isolates. In rhesus macaques both immunogens elicited potent binding antibodies, but again the modified immunogen was more effective in eliciting the generation of neutralizing antibodies against the SF162ΔV2 and SF162 viruses. Antibodies capable of neutralizing several, but not all, heterologous primary HIV-1 isolates tested were elicited only in macaques immunized with the modified immunogen. The efficiency of neutralization of these heterologous isolates was lower than that recorded against the SF162 isolate. Our results strongly suggest that although soluble oligomeric envelope subunit vaccines may elicit neutralizing antibody responses against heterologous primary HIV-1 isolates, these responses will not be broad and potent unless specific modifications are introduced to increase the exposure of conserved neutralization epitopes.
Trypsin Cleavage Stabilizes the Rotavirus VP4 Spike
Authors: Crawford Sue E. , Mukherjee Sharmila K. , Estes Mary K. , Lawton Jeffery A. , Shaw Andrea L. , Ramig Robert F. , Prasad B. V. Venkataram 
Published: July 2002

ABSTRACT

Trypsin enhances rotavirus infectivity by an unknown mechanism. To examine the structural basis of trypsin-enhanced infectivity in rotaviruses, SA11 4F triple-layered particles (TLPs) grown in the absence (nontrypsinized rotavirus [NTR]) or presence (trypsinized rotavirus [TR]) of trypsin were characterized to determine the structure, the protein composition, and the infectivity of the particles before and after trypsin treatment. As expected, VP4 was not cleaved in NTR particles and was cleaved into VP5
∗
and VP8
∗
in TR particles. However, surprisingly, while the VP4 spikes were clearly visible and well ordered in the electron cryomicroscopy reconstructions of TR TLPs, they were totally absent in the reconstructions of NTR TLPs. Biochemical analysis with radiolabeled particles indicated that the stoichiometry of the VP4 in NTR particles was the same as that in TR particles and that the VP8
∗
portion of NTR, but not TR, particles is susceptible to further proteolysis by trypsin. Taken together, these structural and biochemical data show that the VP4 spikes in the NTR TLPs are icosahedrally disordered and that they are conformationally different. Structural studies on the NTR TLPs after trypsin treatment showed that spike structure could be partially recovered. Following additional trypsin treatment, infectivity was enhanced for both NTR and TR particles, but the infectivity of NTR remained 2 logs lower than that of TR particles. Increased infectivity in these particles corresponded to additional cleavages in VP5
∗
, at amino acids 259, 583, and putatively 467, which are conserved in all P serotypes of human and animal group A rotaviruses and also corresponded with a structural change in VP7. These biochemical and structural results show that trypsin cleavage imparts order to VP4 spikes on de novo synthesized virus particles, and these ordered spikes make virus entry into cells more efficient.