bluuebunny/crossref_metadata_2025 huggingface dataset:
Financing and Advising: Optimal Financial Contracts with Venture Capitalists
Authors: Casamatta Catherine
Published: September 2003

This paper analyses the joint provision of effort by an entrepreneur and by an advisor to improve the productivity of an investment project. Without moral hazard, it is optimal that both exert effort. With moral hazard, if the entrepreneur's effort is more efficient (less costly) than the advisor's effort, the latter is not hired if she does not provide funds. Outside financing arises endogenously. This explains why investors like venture capitalists are value enhancing. The level of outside financing determines whether common stocks or convertible bonds should be issued in response to incentives.
Anticompetitive Financial Contracting: The Design of Financial Claims
Authors: Cestone Giacinta , White Lucy
Published: September 2003

This paper presents the first model where entry deterrence takes place through financial rather than product‐market channels. In existing models, a firm's choice of financial instruments deters entry by affecting product market behavior; here entry deterrence occurs by affecting the credit market behavior of investors towards entrant firms. We find that to deter entry, the claims held on incumbent firms should be sufficiently risky, that is, equity. This contrasts with the standard Brander and Lewis (1986) result that debt deters entry. This effect is more marked the less competitive the credit market is—so more credit market competition spurs more product market competition.
Investment, Uncertainty, and Liquidity
Authors: Boyle Glenn W. , Guthrie Graeme A.
Published: September 2003

We analyze the dynamic investment decision of a firm subject to an endogenous financing constraint. The threat of future funding shortfalls lowers the value of the firm's timing options and encourages acceleration of investment beyond the first‐best optimal level. As well as highlighting another way by which capital market frictions can distort investment behavior, this result implies that (1) the sensitivity of investment to cash flow can be greatest for high‐liquidity firms and (2) greater uncertainty has an ambiguous effect on investment.
Asset Trading Volume with Dynamically Complete Markets and Heterogeneous Agents
Authors: Judd Kenneth L. , Kubler Felix , Schmedders Karl
Published: September 2003

Trading volume of infinitely lived securities, such as equity, is generically zero in Lucas asset pricing models with heterogeneous agents. More generally, the end‐of‐period portfolio of all securities is constant over time and states in the generic economy. General equilibrium restrictions rule out trading of equity after an initial period. This result contrasts the prediction of portfolio allocation analyses that portfolio rebalancing motives produce nontrivial trade volume. Therefore, other causes of trade must be present in asset markets with large trading volume.
Hedging in the Possible Presence of Unspanned Stochastic Volatility: Evidence from Swaption Markets
Authors: Fan Rong , Gupta Anurag , Ritchken Peter
Published: September 2003

This paper examines whether higher order multifactor models, with state variables linked solely to underlying LIBOR‐swap rates, are by themselves capable of explaining and hedging interest rate derivatives, or whether models explicitly exhibiting features such as unspanned stochastic volatility are necessary. Our research shows that swaptions and even swaption straddles can be well hedged with LIBOR bonds alone. We examine the potential benefits of looking outside the LIBOR market for factors that might impact swaption prices without impacting swap rates, and find them to be minor, indicating that the swaption market is well integrated with the LIBOR‐swap market.
Enhanced Virulence Mediated by the Murine Coronavirus, Mouse Hepatitis Virus Strain JHM, Is Associated with a Glycine at Residue 310 of the Spike Glycoprotein
Authors: Ontiveros Evelena , Kim Taeg S. , Gallagher Thomas M. , Perlman Stanley
Published: September 2003

The coronavirus, mouse hepatitis virus strain JHM, causes acute and chronic neurological diseases in rodents. Here we demonstrate that two closely related virus variants, both of which cause acute encephalitis in susceptible strains of mice, cause markedly different diseases if mice are protected with a suboptimal amount of an anti-JHM neutralizing antibody. One strain, JHM.SD, caused acute encephalitis, while infection with JHM.IA resulted in no acute disease. Using recombinant virus technology, we found that the differences between the two viruses mapped to the spike (S) glycoprotein and that the two S proteins differed at four amino acids. By engineering viruses that differed by only one amino acid, we identified a serine-to-glycine change at position 310 of the S protein (S310G) that recapitulated the more neurovirulent phenotype. The increased neurovirulence mediated by the virus encoding glycine at position S310 was not associated with a different tropism within the central nervous system (CNS) but was associated with increased lateral spread in the CNS, leading to significantly higher brain viral titers. In vitro studies revealed that S310G was associated with decreased S1-S2 stability and with enhanced ability to mediate infection of cells lacking the primary receptor for JHM (“receptor-independent spread”). These enhanced fusogenic properties of viruses encoding a glycine at position 310 of the S protein may contribute to spread within the CNS, a tissue in which expression of conventional JHM receptors is low.
Exploitation of Microtubule Cytoskeleton and Dynein during Parvoviral Traffic toward the Nucleus
Authors: Suikkanen Sanna , Aaltonen Tuula , Nevalainen Marjukka , Välilehto Outi , Lindholm Laura , Vuento Matti , Vihinen-Ranta Maija
Published: September 2003

Canine parvovirus (CPV), a model virus for the study of parvoviral entry, enters host cells by receptor-mediated endocytosis, escapes from endosomal vesicles to the cytosol, and then replicates in the nucleus. We examined the role of the microtubule (MT)-mediated cytoplasmic trafficking of viral particles toward the nucleus. Immunofluorescence and immunoelectron microscopy showed that capsids were transported through the cytoplasm into the nucleus after cytoplasmic microinjection but that in the presence of MT-depolymerizing agents, viral capsids were unable to reach the nucleus. The nuclear accumulation of capsids was also reduced by microinjection of an anti-dynein antibody. Moreover, electron microscopy and light microscopy experiments demonstrated that viral capsids associate with tubulin and dynein in vitro. Coprecipitation studies indicated that viral capsids interact with dynein. When the cytoplasmic transport process was studied in living cells by microinjecting fluorescently labeled capsids into the cytoplasm of cells containing fluorescent tubulin, capsids were found in close contact with MTs. These results suggest that intact MTs and the motor protein dynein are required for the cytoplasmic transport of CPV capsids and contribute to the accumulation of the capsid in the nucleus.
The Gammaherpesvirus 68 Latency-Associated Nuclear Antigen Homolog Is Critical for the Establishment of Splenic Latency
Authors: Moorman Nathaniel J. , Willer David O. , Speck Samuel H.
Published: September 2003

Open reading frame 73 (ORF 73) is conserved among the gamma-2-herpesviruses (rhadinoviruses) and, in Kaposi's sarcoma-associated herpesvirus (KSHV) and herpesvirus saimiri (HVS), has been shown to encode a latency-associated nuclear antigen (LANA). The KSHV and HVS LANAs have also been shown to be required for maintenance of the viral genome as an episome during latency. LANA binds both the viral latency-associated origin of replication and the host cell chromosome, thereby ensuring efficient partitioning of viral genomes to daughter cells during mitosis of a latently infected cell. In gammaherpesvirus 68 (γHV68), the role of the LANA homolog in viral infection has not been analyzed. Here we report the construction of a γHV68 mutant containing a translation termination codon in the LANA ORF (73.STOP). The 73.STOP mutant virus replicated normally in vitro, in both proliferating and quiescent murine fibroblasts. In addition, there was no difference between wild-type (WT) and 73.STOP virus in the kinetics of induction of lethality in mice lacking B and T cells (Rag 1
−/−
) infected with 1,000 PFU of virus. However, compared to WT virus, the 73.STOP mutant exhibited delayed kinetics of replication in the lungs of immunocompetent C57BL/6 mice. In addition, the 73.STOP mutant exhibited a severe defect in the establishment of latency in the spleen of C57BL/6 mice. Increasing the inoculum of 73.STOP virus partially overcame the acute replication defected observed in the lungs at day 4 postinfection but did not ameliorate the severe defect in the establishment of splenic latency. Thus, consistent with its proposed role in replication of the latent viral episome, LANA appears to be a critical determinant in the establishment of γHV68 latency in the spleen post-intranasal infection.
Antigenic Subclasses of Polytropic Murine Leukemia Virus (MLV) Isolates Reflect Three Distinct Groups of Endogenous Polytropic MLV-Related Sequences in NFS/N Mice
Authors: Evans Leonard H. , Lavignon Marc , Taylor Marc , Alamgir A. S. M.
Published: September 2003

Polytropic murine leukemia viruses (MLVs) are generated by recombination of ecotropic MLVs with members of a family of endogenous proviruses in mice. Previous studies have indicated that polytropic MLV isolates comprise two mutually exclusive antigenic subclasses, each of which is reactive with one of two monoclonal antibodies termed MAb 516 and Hy 7. A major determinant of the epitopes distinguishing the subclasses mapped to a single amino acid difference in the SU protein. Furthermore, distinctly different populations of the polytropic MLV subclasses are generated upon inoculation of different ecotropic MLVs. Here we have characterized the majority of endogenous polytropic MLV-related proviruses of NFS/N mice. Most of the proviruses contain intact sequences encoding the receptor-binding region of the SU protein and could be distinguished by sequence heterogeneity within that region. We found that the endogenous proviruses comprise two major groups that encode the major determinant for Hy 7 or MAb 516 reactivity. The Hy 7-reactive proviruses correspond to previously identified polytropic proviruses, while the 516-reactive proviruses comprise the modified polytropic proviruses as well as a third group of polytropic MLV-related proviruses that exhibit distinct structural features. Phylogenetic analyses indicate that the latter proviruses reflect features of phylogenetic intermediates linking xenotropic MLVs to the polytropic and modified polytropic proviruses. These studies elucidate the relationships of the antigenic subclasses of polytropic MLVs to their endogenous counterparts, identify a new group of endogenous proviruses, and identify distinguishing characteristics of the proviruses that should facilitate a more precise description of their expression in mice and their participation in recombination to generate recombinant viruses.
Genome of Bovine Herpesvirus 5
Authors: Delhon G. , Moraes M. P. , Lu Z. , Afonso C. L. , Flores E. F. , Weiblen R. , Kutish G. F. , Rock D. L.
Published: September 2003

Here we present the complete genomic sequence of bovine herpesvirus 5 (BHV-5), an alphaherpesvirus responsible for fatal meningoencephalitis in cattle. The 138,390-bp genome encodes 70 putative proteins and resembles the α2 subgroup of herpesviruses in genomic organization and gene content. BHV-5 is very similar to BHV-1, the etiological agent of infectious bovine rhinotracheitis, as reflected by the high level of amino acid identity in their protein repertoires (average, 82%). The highest similarity to BHV-1 products (≥95% amino acid identity) is found in proteins involved in viral DNA replication and processing (UL5, UL15, UL29, and UL39) and in virion proteins (UL14, UL19, UL48, and US6). Among the least conserved (≤75%) are the homologues of immediate-early (IE) proteins BICP0, BICP4, and BICP22, the three proteins being longer in BHV-5 than in BHV-1. The structure of the BHV-5 latency-related (LR) region departs markedly from that of BHV-1 in both coding and transcriptional regulatory regions. Given the potential significance of IE genes and the LR region in virus-neuron interactions, it is likely these differences contribute to BHV-5 neuropathogenicity.
Cellular Immunity Elicited by Human Immunodeficiency Virus Type 1/ Simian Immunodeficiency Virus DNA Vaccination Does Not Augment the Sterile Protection Afforded by Passive Infusion of Neutralizing Antibodies
Authors: Mascola John R. , Lewis Mark G. , VanCott Thomas C. , Stiegler Gabriela , Katinger Hermann , Seaman Michael , Beaudry Kristin , Barouch Dan H. , Korioth-Schmitz Birgit , Krivulka Georgia , Sambor Anna , Welcher Brent , Douek Daniel C. , Montefiori David C. , Shiver John W. , Poignard Pascal , Burton Dennis R. , Letvin Norman L.
Published: September 2003

High levels of infused anti-human immunodeficiency virus type 1 (HIV-1) neutralizing monoclonal antibodies (MAbs) can completely protect macaque monkeys against mucosal chimeric simian-human immunodeficiency virus (SHIV) infection. Antibody levels below the protective threshold do not prevent infection but can substantially reduce plasma viremia. To assess if HIV-1/SIV-specific cellular immunity could combine with antibodies to produce sterile protection, we studied the effect of a suboptimal infusion of anti-HIV-1 neutralizing antibodies in macaques with active cellular immunity induced by interleukin-2 (IL-2)-adjuvanted DNA immunization. Twenty female macaques were divided into four groups: (i) DNA immunization plus irrelevant antibody, (ii) DNA immunization plus infusion of neutralizing MAbs 2F5 and 2G12, (iii) sham DNA plus 2F5 and 2G12, and (iv) sham DNA plus irrelevant antibody. DNA-immunized monkeys developed CD4 and CD8 T-cell responses as measured by epitope-specific tetramer staining and by pooled peptide ELISPOT assays for gamma interferon-secreting cells. After vaginal challenge, DNA-immunized animals that received irrelevant antibody became SHIV infected but displayed lower plasma viremia than control animals. Complete protection against SHIV challenge occurred in three animals that received sham DNA plus MAbs 2F5 and 2G12 and in two animals that received the DNA vaccine plus MAbs 2F5 and 2G12. Thus, although DNA immunization produced robust HIV-specific T-cell responses, we were unable to demonstrate that these responses contributed to the sterile protection mediated by passive infusion of neutralizing antibodies. These data suggest that although effector T cells can limit viral replication, they are not able to assist humoral immunity to prevent the establishment of initial infection.
Identification of Adenovirus (Ad) Penton Base Neutralizing Epitopes by Use of Sera from Patients Who Had Received Conditionally Replicative Ad (Ad
dl
1520) for Treatment of Liver Tumors
Authors: Hong Saw See , Habib Nagy A. , Franqueville Laure , Jensen Steen , Boulanger Pierre A.
Published: September 2003

Sera from 17 patients with primary and secondary liver tumors who had been administered oncolytic adenovirus (Ad) mutant Ad
dl
1520 were analyzed for anti-Ad neutralization titers and antibodies to the Ad major capsid proteins hexon, penton base (Pb), and fiber. The antibodies recognized mainly conformational epitopes in hexon and both linear and conformational epitopes in Pb and fiber. Pb-specific antibodies were isolated from serum samples that had been obtained prior to and during the course of the treatment of four of these patients. We found that the Pb antibodies had a significant contribution toward anti-Ad neutralization, and this mainly occurred at the step of virus internalization. The Pb antigenic epitopes were determined by phage biopanning and were mapped to 10 discrete regions, which made up three major immunodominant domains within residues 51 to 120, 193 to 230, and 311 to 408, respectively. One of these domains (residues 311 to 408) overlapped the highly conserved, integrin-binding RGD (Arg-Gly-Asp) motif. The contribution of antibodies directed to RGD and other epitopes in Ad neutralization activity was determined indirectly by using a phage-mediated depletion assay. Our results suggested that circulating RGD antibodies were not prevalent and were poorly neutralizing and that other peptide motifs within residues 51 to 60, 216 to 226, and 311 to 408 in Pb sequence represented major target sites for neutralizing antibodies.
Characterization of the Rhesus Cytomegalovirus US28 Locus
Authors: Penfold M. E. T. , Schmidt T. L. , Dairaghi D. J. , Barry P. A. , Schall T. J.
Published: September 2003

Human cytomegalovirus (CMV) US28 (and the related open reading frame [ORF] US27) are G-protein-coupled receptor homologs believed to play a role in viral pathogenesis. In vitro, US28 has been shown to bind and internalize ligands, as well as activate intracellular signaling in response to certain chemokines, and to initiate the migration of smooth muscle cells to chemokine gradients. To assess the role of US28 in vivo, we examined the rhesus model and sequenced and characterized the rhesus CMV US28 locus. We found that rhesus CMV carries five tandem homologs of US28, all widely divergent from US28 and from each other. By reverse transcription-PCR and Northern analysis, we demonstrated expression of these ORFs in infected cells. With stable cell lines expressing these ORFs, we analyzed the homolog's binding and signaling characteristics across a wide range of chemokines and found one (RhUS28.5) to have a ligand binding profile similar to that of US28. In addition, we localized US28 and the rhesus CMV homolog RhUS28.5 to the envelope of infectious virions, suggesting a role in viral entry or cell tropism.
Transcription Program of Murine Gammaherpesvirus 68
Authors: Martinez-Guzman DeeAnn , Rickabaugh Tammy , Wu Ting-Ting , Brown Helen , Cole Steven , Song Moon Jung , Tong Leming , Sun Ren
Published: September 2003

Murine gammaherpesvirus 68 (MHV-68 [also referred to as γHV68]) is phylogenetically related to Kaposi's sarcoma-associated herpesvirus (KSHV [also referred to as HHV-8]) and Epstein-Barr virus (EBV). However, unlike KSHV or EBV, MHV-68 readily infects fibroblast and epithelial cell lines derived from several mammalian species, providing a system to study productive and latent infections as well as reactivation of gammaherpesviruses in vivo and in vitro. To carry out rapid genome-wide analysis of MHV-68 gene expression, we made DNA arrays containing nearly all of the known and predicted open reading frames (ORFs) of the virus. RNA obtained from an MHV-68 latently infected cell line, from cells lytically infected with MHV-68 in culture, and from the lung tissue of infected mice was used to probe the MHV-68 arrays. Using a tightly latent B-cell line (S11E), the MHV-68 latent transcription program was quantitatively described. Using BHK-21 cells and infected mice, we demonstrated that latent genes are transcribed during lytic replication and are relatively independent of de novo protein synthesis. We determined that the transcription profiles at the peak of lytic gene expression are similar in cultured fibroblast and in the lung of infected mice. Finally, the MHV-68 DNA arrays were used to examine the gene expression profile of a recombinant virus that overexpresses replication and transcription activator (RTA), C-RTA/MHV-68, during lytic replication in cell culture. The recombinant virus replicates faster then the parental strain and the DNA arrays revealed that nearly every MHV-68 ORF examined was activated by RTA overexpression. Examination of the gene expression patterns of C-RTA/MHV-68 over a time course led to the finding that the M3 promoter is RTA responsive in the absence of other viral factors.
Evolutionary Pressure of a Receptor Competitor Selects Different Subgroup A Avian Leukosis Virus Escape Variants with Altered Receptor Interactions
Authors: Melder Deborah C. , Pankratz V. Shane , Federspiel Mark J.
Published: September 2003

A complex interaction between the retroviral envelope glycoproteins and a specific cell surface protein initiates viral entry into cells. The avian leukosis-sarcoma virus (ALV) group of retroviruses provides a useful experimental system for studying the retroviral entry process and the evolution of receptor usage. In this study, we demonstrate that evolutionary pressure on subgroup A ALV [ALV(A)] entry exerted by the presence of a competitive inhibitor, a soluble form of the ALV(A) Tva receptor linked to a mouse immunoglobulin G tag (quail sTva-mIgG), can select different populations of escape variants. This escape population contained three abundant ALV(A) variant viruses, all with mutations in the surface glycoprotein hypervariable regions: a previously identified variant containing the Y142N mutation in the hr1 region; a new variant with two mutations, W141G in hr1 and K261E in vr3; and another new variant with two mutations, W145R in hr1 and K261E. The W141G K261E and W145R K261E viruses escape primarily by lowering their binding affinities for the quail Tva receptor competitive inhibitor while retaining wild-type levels of binding affinity for the chicken Tva receptor. A secondary phenotype of the new variants was an alteration in receptor interference patterns from that of wild-type ALV(A), indicating that the mutant glycoproteins are possibly interacting with other cellular proteins. One result of these altered interactions was that the variants caused a transient period of cytotoxicity. We could also directly demonstrate that the W141G K261E variant glycoproteins bound significant levels of a soluble form of the Tvb
S3
ALV receptor in a binding assay. Alterations in the normally extreme specificity of the ALV(A) glycoproteins for Tva may represent an evolutionary first step toward expanding viral receptor usage in response to inefficient viral entry.
Biochemical and Genetic Characterizations of a Novel Human Immunodeficiency Virus Type 1 Inhibitor That Blocks gp120-CD4 Interactions
Authors: Guo Qi , Ho Hsu-Tso , Dicker Ira , Fan Li , Zhou Nannan , Friborg Jacques , Wang Tao , McAuliffe Brian V. , Wang Hwei-gene Heidi , Rose Ronald E. , Fang Hua , Scarnati Helen T. , Langley David R. , Meanwell Nicholas A. , Abraham Ralph , Colonno Richard J. , Lin Pin-fang
Published: September 2003

BMS-378806 is a recently discovered small-molecule human immunodeficiency virus type 1 (HIV-1) attachment inhibitor with good antiviral activity and pharmacokinetic properties. Here, we demonstrate that the compound targets viral entry by inhibiting the binding of the HIV-1 envelope gp120 protein to cellular CD4 receptors via a specific and competitive mechanism. BMS-378806 binds directly to gp120 at a stoichiometry of approximately 1:1, with a binding affinity similar to that of soluble CD4. The potential BMS-378806 target site was localized to a specific region within the CD4 binding pocket of gp120 by using HIV-1 gp120 variants carrying either compound-selected resistant substitutions or gp120-CD4 contact site mutations. Mapping of resistance substitutions to the HIV-1 envelope, and the lack of compound activity against a CD4-independent viral infection confirm the gp120-CD4 interactions as the target in infected cells. BMS-378806 therefore serves as a prototype for this new class of antiretroviral agents and validates gp120 as a viable target for small-molecule inhibitors.
Glycoprotein of Nonpathogenic Rabies Viruses Is a Key Determinant of Human Cell Apoptosis
Authors: Préhaud Christophe , Lay Stéphanie , Dietzschold Bernhard , Lafon Monique
Published: September 2003

We showed that, unlike pathogenic rabies virus (RV) strain CVS, attenuated RV strain ERA triggers the caspase-dependent apoptosis of human cells. Furthermore, we observed that the induction of apoptosis is correlated with a particular virus antigen distribution: the overexpression of the viral G protein on the cell surface, with continuous localization on the cytoplasmic membrane, and large cytoplasmic inclusions of the N protein. To determine whether one of these two major RV proteins (G and N proteins) triggers apoptosis, we constructed transgenic Jurkat T-cell lines that drive tetracycline-inducible gene expression to produce the G and N proteins of ERA and CVS individually. The induction of ERA G protein (G-ERA) expression but not of ERA N protein expression resulted in apoptosis, and G-ERA was more efficient at triggering apoptosis than was CVS G protein. To test whether other viral proteins participated in the induction of apoptosis, human cells were infected with recombinant RV in which the G protein gene from the attenuated strain had been replaced by its virulent strain counterpart (CVS). Only RV containing the G protein from the nonpathogenic RV strain was able to trigger the apoptosis of human cells. Thus, the ability of RV strains to induce apoptosis is largely determined by the viral G protein.
Direct Activation of Cyclin-Dependent Kinase 2 by Human Papillomavirus E7
Authors: He Wanxia , Staples Doug , Smith Clark , Fisher Chris
Published: September 2003

Addition of human papillomavirus (HPV) E7 CDK2/cyclin A or CDK2/cyclin E, purified from either insect cells or bacteria, dramatically upregulates histone H1 kinase activity. Activation is substrate specific, with a smaller effect noted for retinoblastoma protein (Rb). The CDK2 stimulatory activity is equivalent in high-risk (HPV type 16 [HPV16] and HPV31) and low-risk (HPV6b) E7. Mutational analyses of HPV16 E7 indicate that the major activity resides in amino acids 9 to 38, spanning CR1 and CR2, and does not require casein kinase II or Rb-binding domain functions. Synthetic peptides spanning HPV16 amino acid residues 9 to 38 also activate CDK2. Peptides containing this sequence that carry biotin on the carboxy terminus, as well as a photoactivated cross-linking group (benzophenone), also activate the complex and covalently associate with the CDK2/cyclin A complex in a specific manner requiring UV. Cross-linking studies that use protein monomers detect association of the E7 peptides with cyclin A but not CDK2. Together, our results indicate a novel mechanism whereby E7 promotes HPV replication by directly altering CDK2 activity and substrate specificity.
Multiple Type A/B Heterogeneous Nuclear Ribonucleoproteins (hnRNPs) Can Replace hnRNP A1 in Mouse Hepatitis Virus RNA Synthesis
Authors: Shi Stephanie T. , Yu Guann-Yi , Lai Michael M. C.
Published: September 2003

Heterogeneous nuclear ribonucleoprotein (hnRNP) A1 has previously been shown to bind mouse hepatitis virus (MHV) RNA at the 3′ end of both plus and minus strands and modulate MHV RNA synthesis. However, a mouse erythroleukemia cell line, CB3, does not express hnRNP A1 but still supports MHV replication, suggesting that alternative proteins can replace hnRNP A1 in cellular functions and viral infection. In this study, we set out to identify these proteins. UV cross-linking experiments revealed that several CB3 cellular proteins similar in size to hnRNP A1 interacted with the MHV RNA. These proteins were purified by RNA affinity column with biotinylated negative-strand MHV leader RNA and identified by mass spectrometry to be hnRNP A2/B1, hnRNP A/B, and hnRNP A3, all of which belong to the type A/B hnRNPs. All of these proteins contain amino acid sequences with strong similarity to the RNA-binding domains of hnRNP A1. Some of these hnRNPs have previously been shown to replace hnRNP A1 in regulating RNA splicing. These proteins displayed MHV RNA-binding affinity and specificity similar to those of hnRNP A1. hnRNP A2/B1, which is predominantly localized to the nucleus and shuttles between the nucleus and the cytoplasm, was shown to relocalize to the cytoplasm in MHV-infected CB3 cells. Furthermore, overexpression of hnRNP A/B in cells enhanced MHV RNA synthesis. Our findings demonstrate that the functions of hnRNP A1 in MHV RNA synthesis can be replaced by other closely related hnRNPs, further supporting the roles of cellular proteins in MHV RNA synthesis.
Differences in Virus-Induced Cell Morphology and in Virus Maturation between MVA and Other Strains (WR, Ankara, and NYCBH) of Vaccinia Virus in Infected Human Cells
Authors: Gallego-Gómez Juan Carlos , Risco Cristina , Rodríguez Dolores , Cabezas Pilar , Guerra Susana , Carrascosa José L. , Esteban Mariano
Published: September 2003

Live recombinants based on attenuated modified vaccinia virus Ankara (MVA) are potential vaccine candidates against a broad spectrum of diseases and tumors. To better understand the efficacy of MVA as a human vaccine, we analyzed by confocal and electron microscopy approaches MVA-induced morphological changes and morphogenetic stages during infection of human HeLa cells in comparison to other strains of vaccinia virus (VV): the wild-type Western Reserve (WR), Ankara, and the New York City Board of Health (NYCBH) strains. Confocal microscopy studies revealed that MVA infection alters the cytoskeleton producing elongated cells (bipolar), which do not form the characteristic actin tails. Few virions are detected in the projections connecting neighboring cells. In contrast, cells infected with the WR, Ankara, and NYCBH strains exhibit a stellated (multipolar) or rounded morphology with actin tails. A detailed transmission electron microscopy analysis of HeLa cells infected with MVA showed important differences in fine ultrastructure and amounts of the viral intermediates compared to cells infected with the other VV strains. In HeLa cells infected with MVA, the most abundant viral forms are intracellular immature virus, with few intermediates reaching the intracellular mature virus (IMV) form, at various stages of maturation, which exhibit a more rounded shape than IMVs from cells infected with the other VV strains. The “IMVs” from MVA-infected cells have an abnormal internal structure (“atypical” viruses) with potential alterations in the core-envelope interactions and are unable to significantly acquire the additional double envelope to render intracellular envelope virus. The presence of potential cell-associated envelope virus is very scarce. Our findings revealed that MVA in human cells promotes characteristic morphological changes to the cells and is able to reach the IMV stage, but these virions were not structurally normal and the subsequent steps in the morphogenetic pathway are blocked.
Significance in Replication of the Terminal Nucleotides of the
Flavivirus
Genome
Authors: Khromykh Alexander A , Kondratieva Natasha , Sgro Jean-Yves , Palmenberg Ann , Westaway Edwin G
Published: September 2003

Point mutations that resulted in a substitution of the conserved 3′-penultimate cytidine in genomic RNA or the RNA negative strand of the self-amplifying replicon of the
Flavivirus Kunjin virus
completely blocked in vivo replication. Similarly, substitutions of the conserved 3′-terminal uridine in the RNA negative or positive strand completely blocked replication or caused much-reduced replication, respectively. The same preference for cytidine in the 3′-terminal dinucleotide was noted in reports of the in vitro activity of the RNA-dependent RNA polymerase (RdRp) for the other genera of
Flaviviridae
that also employ a double-stranded RNA (dsRNA) template to initiate asymmetric semiconservative RNA positive-strand synthesis. The
Kunjin virus
replicon results were interpreted in the context of a proposed model for initiation of RNA synthesis based on the solved crystal structure of the RdRp of φ6 bacteriophage, which also replicates efficiently using a dsRNA template with conserved 3′-penultimate cytidines and a 3′-terminal pyrimidine. A previously untested substitution of the conserved pentanucleotide at the top of the 3′-terminal stem-loop of all
Flavivirus
species also blocked detectable in vivo replication of the
Kunjin virus
replicon RNA.
Cell-Derived Sequences in the N-Terminal Region of the Polyprotein of a Cytopathogenic Pestivirus
Authors: Müller A. , Rinck G. , Thiel H.-J. , Tautz N.
Published: September 2003

Efficient proteolytic release of nonstructural protein 3 (NS3) from the viral polyprotein is considered to be crucial for the cytopathogenicity of pestiviruses. Here we describe a novel cytopathogenic (cp) bovine viral diarrhea virus strain (BVDV CP8) with a complex insertion composed of viral and cell-derived sequences, including two fragments of the cellular J-domain protein Jiv (J-domain protein interacting with viral protein) located in the N-terminal region of the polyprotein. BVDV CP8 expresses a Jiv fusion protein of 513 amino acids in addition to a complete set of viral proteins. This protein has the capacity to induce NS2-3 cleavage intrans. Accordingly, CP8 is a representative of a novel type of cp pestivirus with a cp-specific mutation located outside of the NS2-3 gene.
CD81-Dependent Binding of Hepatitis C Virus E1E2 Heterodimers
Authors: Cocquerel Laurence , Kuo Chiung-Chi , Dubuisson Jean , Levy Shoshana
Published: September 2003

Hepatitis C virus (HCV) is the leading cause of chronic liver disease worldwide. HCV is also the major cause of mixed cryoglobulinemia, a B-lymphocyte proliferative disorder. Direct experimentation with native viral proteins is not feasible. Truncated versions of recombinant E2 envelope proteins, used as surrogates for viral particles, were shown to bind specifically to human CD81. However, truncated E2 may not fully mimic the surface of HCV virions because the virus encodes two envelope glycoproteins that associate with each other as E1E2 heterodimers. Here we show that E1E2 complexes efficiently bind to CD81 whereas truncated E2 is a weak binder, suggesting that truncated E2 is probably not the best tool with which to study cellular interactions. To gain better insight into virus-cell interactions, we developed a method by which to isolate E1E2 complexes that are properly folded. We demonstrate that purified E1E2 heterodimers bind to cells in a CD81-dependent manner. Furthermore, engagement of B cells by purified E1E2 heterodimers results in their aggregation and in protein tyrosine phosphorylation, a hallmark of B-cell activation. These studies provide a possible clue to the etiology of HCV-associated B-cell lymphoproliferative diseases. They also delineate a method by which to isolate biologically functional E1E2 complexes for the study of virus-host cell interaction in other cell types.
Lassa Virus Z Protein Is a Matrix Protein Sufficient for the Release of Virus-Like Particles
Authors: Strecker Thomas , Eichler Robert , Meulen Jan ter , Weissenhorn Winfried , Dieter Klenk Hans , Garten Wolfgang , Lenz Oliver
Published: September 2003

Lassa virus is an enveloped virus with glycoprotein spikes on its surface. It contains an RNA ambisense genome that encodes the glycoprotein precursor GP-C, the nucleoprotein NP, the polymerase L, and the Z protein. Here we demonstrate that the Lassa virus Z protein (i) is abundant in viral particles, (ii) is strongly membrane associated, (iii) is sufficient in the absence of all other viral proteins to release enveloped particles, and (iv) contains two late domains, PTAP and PPXY, necessary for the release of virus-like particles. Our data provide evidence that Z is the Lassa virus matrix protein that is the driving force for virus particle release.
Ballast-mediated animal introductions in the Laurentian Great Lakes: retrospective and prospective analyses
Authors: Grigorovich Igor A , Colautti Robert I , Mills Edward L , Holeck Kristen , Ballert Albert G , MacIsaac Hugh J
Published: September 2003

Since completion of the St. Lawrence Seaway in 1959, at least 43 nonindigenous species (NIS) of animals and protists have established in the Laurentian Great Lakes, of which ~67% were attributed to discharge of ballast water from commercial ships. Twenty-three NIS were first discovered in four "hotspot" areas with a high representation of NIS, most notably the Lake Huron  Lake Erie corridor. Despite implementation of the voluntary (1989, Canada) and mandatory (1993, U.S.A.) ballast water exchange (BWE) regulations, NIS were discovered at a higher rate during the 1990s than in the preceding three decades. Here we integrate knowledge of species' invasion histories, shipping traffic patterns, and physicochemical factors that constrain species' survivorship during ballast-mediated transfer to assess the risk of future introductions to the Great Lakes. Our risk-assessment model identified 26 high-risk species that are likely to survive intercontinental transfer in ballast tanks. Of these, 10 species have already invaded the Great Lakes. An additional 37 lower-risk species, of which six have already invaded, show some but not all attributes needed for successful introduction under current BWE management. Our model indicates that the Great Lakes remain vulnerable to ship-mediated NIS invasions.
Change in biomass of benthic and planktonic algae along a disturbance gradient for 24 Great Lakes coastal wetlands
Authors: McNair Sheila A , Chow-Fraser Patricia
Published: September 2003

We quantified the chlorophyll a content of planktonic algae and benthic algae in periphyton on acrylic rods and in epiphyton growing on macrophytes in 24 coastal wetlands in all five Laurentian Great Lakes. Sites were selected to represent a wide range of environmental conditions ranging from nutrient-poor, clear-water marshes with abundant macrophytes to nutrient-enriched, turbid systems devoid of aquatic vegetation. Water quality and species and percent cover of submergent macrophytes were measured in each wetland. Principal components analysis (PCA) showed that total phosphorus, turbidity, and suspended solids, variables associated with human-induced degradation, were most strongly correlated with PC axis 1 (PC1), accounting for 69% of the total variation. The PC1 site score was significantly related to both periphyton and phytoplankton biomass, respectively accounting for 54 and 70% of the total variation in periphyton and phytoplankton data, whereas PC1 only accounted for 18% of the variation in epiphyton biomass. Periphytic and epiphytic biomass were negatively correlated with percent cover and species richness of submergent macrophytes, but phytoplankton biomass was not. We conclude that periphytic and planktonic chlorophyll a biomass are good indicators of human-induced water-quality degradation and recommend that both benthic and planktonic algal biomass should be routinely monitored as part of an effective wetland management program.
Fish recruitment on floodplains: the roles of patterns of flooding and life history characteristics
Authors: King A J , Humphries P , Lake P S
Published: September 2003

Floodplain inundation in rivers is thought to enhance fish recruitment by providing a suitable spawning environment and abundant food and habitat for larvae. Although this model has not previously been tested in Australian rivers, it is often extrapolated to fishes of the Murray-Darling Basin. Fortnightly sampling of larvae and juveniles was conducted in the unregulated Ovens River floodplain during springsummer of 1999 (non-flood year) and 2000 (flood year). The only species that increased in larval abundance during or shortly after flooding was an introduced species, common carp (Cyprinus carpio). Additionally, the peak abundance of larvae on the floodplain occurred during a rapidly declining hydrograph under low flow conditions in isolated billabongs and anabranches. The low use of the inundated floodplain for recruitment contradicts previous models. We propose a model of the optimum environmental conditions required for use of the inundated floodplain for fish recruitment. The model suggests that the notion of the flood pulse alone controlling fish recruitment is too simplistic to describe all strategies within a system. Rather, the life history adaptations in the fauna of the system and aspects of the hydrological regime such as duration and timing of inundation will control the response of a river's fish fauna to flooding.
Functional link between foraging performance, functional morphology, and diet shift in roach (Rutilus rutilus)
Authors: Hjelm Joakim , van de Weerd Gerco H , Sibbing Ferdinand A
Published: September 2003

This study explores how feeding performance (size-dependent attack rate) and the diet shift from zooplankton to benthic macroinvertebrates in the fish species roach (Rutilus rutilus L.) is related to changes in functional morphology over ontogeny. The morphological changes included overall body shape and structures of the feeding apparatus. The foraging performance of roach on zooplankton, as a function of size, was hump-shaped with a maximum of ~160 mm, and the diet shift took place around 150 mm. Over ontogeny, roach body shape gradually changed from fusiform into high-bodied. The second principal component (PC2) of the feeding apparatus had a U-shaped relationship with body size, with a minimum at 140-mm total length, which is the inverse of that found for the foraging performance on zooplankton. We suggest that changes of the feeding apparatus affect prey intake during the early zooplanktivorous phases and at the final benthivorous feeding stage, whereas prey retention ability limits the maximum intake rate at a later phase of the zooplanktivorous feeding stage. Our results also suggest the presence of both positive and negative correlations in morphology between the feeding niches, which point to the occurrence of morphological trade-offs within ontogenetic niches.
Resistance, resilience, and patchiness of invertebrate assemblages in native tussock and pasture streams in New Zealand after a hydrological disturbance
Authors: Melo Adriano S , Niyogi Dev K , Matthaei Christoph D , Townsend Colin R
Published: September 2003

We generated hydrological disturbances to investigate the role of disturbance in New Zealand streams in two land uses: native tussock grasslands and exotic pasture catchments. We tested whether physical differences in streambed structure confer higher resistance and resilience in tussock sites than in pasture sites. We also investigated changes in patchiness (at spatial scales larger than 0.06 m2) caused by the disturbance. Invertebrate abundance decreased immediately after the disturbance. Species density remained unchanged, but species richness (rarefied) increased. Eight days after the disturbance event, abundance and species richness (rarefied) were similar to those of samples collected immediately before the disturbance. Resistance (measured as decrease in abundance) and resilience (measured as recovery within 8 days) did not differ significantly between the land uses. Patchiness increased in both stream types immediately after the disturbance but decreased to predisturbance levels after 8 days. Disturbance caused a redistribution of individuals among patches, some receiving individuals, others losing individuals, and some remaining unchanged. Our results conform with predictions of the patch dynamics concept and are consistent with results of studies of natural disturbance caused by floods.
Climate change: the potential for latitudinal effects on algal biomass in aquatic ecosystems
Authors: Flanagan Kyla M , McCauley Edward , Wrona Frederick , Prowse Terry
Published: September 2003

Arctic aquatic systems are considered to be highly susceptible to climate change. Both increases in temperature and nutrient input would be anticipated to alter primary production within these lakes. Consequently, understanding the current relationship between nutrients and productivity is crucial for predicting the effects of climate change. In this paper, we synthesize published data on algal biomass, total phosphorus, total nitrogen, maximum depth, altitude, longitude, and latitude to determine whether average algal biomass differs for temperate and arctic lakes. A total of 57 sources were used, resulting in data for 433 lake-years, ranging in latitudes from 41 to 79°N. Average algal biomass observed during the ice-free season increased significantly with phosphorous levels, but the latitude of the system had a significant negative impact on algal biomass. We briefly outline two major hypotheses, based on existing empirical evidence, for the lower algal yield found in higher latitude systems. The first hypothesis discusses bottom-up control and the influence of abiotic factors on algal biomass. The second hypothesis relates to food chain composition and top-down influences. The latitudinal effect on algal yield suggests that arctic lakes could dramatically increase in productivity if these systems experience increases in temperature and nutrient concentrations as predicted by climate change models.
Distributions of physonect siphonulae in the Gulf of Maine and their potential as important sources of acoustic scattering
Authors: Benfield Mark C , Lavery Andone C , Wiebe Peter H , Greene Charles H , Stanton Timothy K , Copley Nancy J
Published: September 2003

The distributions of siphonulae stages of physonect siphonophores were mapped in Wilkinson, Jordan, and Georges basins of the Gulf of Maine using a video plankton recorder. Siphonulae are often overlooked in net samples and our optical survey appears to be the first in situ investigation of these organisms. Siphonulae were distributed at mid-depths in narrow horizontal layers, suggesting potential control of their buoyancy. The siphonulae possessed gas-filled pneumatophores with diameters of 0.10.4 mm. Pneumatophore diameters appeared to be similar over their entire sampled depth range, suggesting that siphonulae may be capable of regulating the pressure of gas within the pneumatophore to maintain a constant volume. The dimensions of the siphonulae pneumatophores placed them near the acoustic resonance region for scattering at 43 kHz when near the surface and 120 kHz when at depth. Theoretical estimates of the acoustical target strengths of gas bubbles of sizes corresponding to the sizes of our measured pneumatophores produced relatively strong backscatter. Layers of siphonulae corresponded to regions of high acoustical backscatter at 120, 200, and 420 kHz.
On the distribution of the European eel (Anguilla anguilla) and its fisheries
Authors: Dekker Willem
Published: September 2003

For the distribution of the European eel (Anguilla anguilla), only Schmidt (1909) has conducted substantial investigations, yielding a qualitative description (Atlantic and Mediterranean coasts of Europe and Northern Africa). In this article, a meta-analysis of reported fishing yields is presented, showing a major concentration of glass eel yield in the Bay of Biscay (and possibly farther south) and of yellow and (or) silver eel yield in the western Mediterranean. Fisheries target the glass eel stage at highest stock density and shift to the silver eel stage at low density. Because there is no suitable habitat in the Sahara, the southern limit is, contrary to Schmidt's belief, primarily determined by continental conditions. From the centre of the distribution to the north, a long and slow decline in density occurs. The mismatch between northern temperatures and the species' preference, in combination with the very low abundance, indicates that the European eel is best seen as a warm-water species, like most other eel species (Anguilla spp.), showing a considerable northern diaspora.