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At least 73 records · Page 4Linked to original sources
PubMed1988

Transition from initiation to elongation in protein-primed phi 29 DNA replication: salt-dependent stimulation by the viral protein p6.

The transition step from the p3-dAMP initiation complex to the first elongated products, p3-(dAMP)2 and p3-(dAMP)3, requires a dATP concentration higher than that needed for the initiation reaction or for the further elongation of the p3-(dAMP)3 complex. The elongation in phi 29 DNA-protein p3 replication in vitro was strongly inhibited by salt. Under inhibitory salt concentration, the viral protein p6 greatly stimulated phi 29 DNA-protein p3 replication. The effect of protein p6 was not on the rate of elongation but on the amount of elongated product, stimulating the transition from initiation to formation of the first elongation products.

Bacteriophages↗
PubMed1975

Chromatographic separation and antigenic analysis of proteins of the oncornaviruses. V. Identification of a new murine viral protein, p15(E).

Profiling of murine leukemia virus (MuLV) proteins by polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate (SDS-PAGE) has revealed a low-molecular-weight protein which does not appear in the corresponding region of viral protein profiles obtained by gel filtration in 6 M guanidine hydrochloride. This protein species, termed p15(E), is easily demonstrable in MuLV isolates for which the viral p15 and p12 proteins have almost identical electrophoretic mobilities; this leaves a protein slightly larger than these two in the PAGE system unaccounted for in the gel filtration system. However, antiserum against the void volume fraction of the gel filtration eluate precipitated the p15(E) component from solubilized, radiolabeled virions, as shown by SDS-PAGE analysis of such immunoprecipitates. Comparative radioprecipitation analyses of this type revealed that for various MuLV isolates p15(E) was distinguishable from p15 in terms of serological reactivities, relative mobilities in gel electrophoresis, and relative efficiencies of labeling with individual amino acids. Thus it appears that, as is the case for avian oncornaviruses, MuLVs contain seven major structural proteins.

Animals↗
PubMed2004

Heat shock protein 70 protects cells from cell cycle arrest and apoptosis induced by human immunodeficiency virus type 1 viral protein R.

Viral protein R (Vpr) of human immunodeficiency virus type 1 (HIV-1) is an accessory protein that plays an important role in viral pathogenesis. This pathogenic activity of Vpr is related in part to its capacity to induce cell cycle G2 arrest and apoptosis of target T cells. A screening for multicopy suppressors of these Vpr activities in fission yeast identified heat shock protein 70 (Hsp70) as a suppressor of Vpr-induced cell cycle arrest. Hsp70 is a member of a family of molecular chaperones involved in innate immunity and protection from environmental stress. In this report, we demonstrate that HIV-1 infection induces Hsp70 in target cells. Overexpression of Hsp70 reduced the Vpr-dependent G2 arrest and apoptosis and also reduced replication of the Vpr-positive, but not Vpr-deficient, HIV-1. Suppression of Hsp70 expression by RNA interference (RNAi) resulted in increased apoptosis of cells infected with a Vpr-positive, but not Vpr-defective, HIV-1. Replication of the Vpr-positive HIV-1 was also increased when Hsp70 expression was diminished. Vpr and Hsp70 coimmunoprecipitated from HIV-infected cells. Together, these results identify Hsp70 as a novel anti-HIV innate immunity factor that targets HIV-1 Vpr.

Apoptosis↗
PubMed1985

Maturation of murine leukemia virus env proteins in the absence of other viral proteins.

A mutant of Akv which produces env but no detectable gag or pol products (A. Rein, D. R. Lowy, B. I. Gerwin, S. K. Ruscetti, and R. H. Bassin, J. Virol. 41, 626-634 (1982] was examined for maturation of env gene protein products. In comparison with wild-type Akv, the mutant AK 71 synthesizes gPr85env and produces gp70 and Prp15E in normal amounts and with normal kinetics. Cell surface gp70 was found alike in the mutant and wild type. However, cleavage of Pr15E to p15E did not occur in the mutant. This final cleavage step of AK 71 Prp15E could be made to occur by superinfecting cells containing the mutant with baboon endogenous virus. Thus, unlike earlier steps, this final step in maturation of the env gene product appears to require gag or pol gene products. It is proposed that the virus-encoded protease is required for this last step.

Animals↗
PubMed2006

Cytobiological consequences of calcium-signaling alterations induced by human viral proteins.

Since calcium-signaling regulates specific and fundamental cellular processes, it represents the ideal target of viral proteins, in order for the virus to control cellular functions and favour its persistence, multiplication and spread. A detailed analysis of reports focused on the impact of viral proteins on calcium-signaling has shown that virus-related elevations of cytosolic calcium levels allow increased viral protein expression (HIV-1, HSV-1/2), viral replication (HBx, enterovirus 2B, HTLV-1 p12(I), HHV-8, EBV), viral maturation (rotavirus), viral release (enterovirus 2B) and cell immortalization (EBV). Interestingly, virus-induced decreased cytosolic calcium levels have been found to be associated with inhibition of immune cells functions (HIV-1 Tat, HHV-8 K15, EBV LMP2A). Finally, several viral proteins are able to modulate intracellular calcium-signaling to control cell viability (HIV-1 Tat, HTLV-1 p13(II), HCV core, HBx, enterovirus 2B, HHV-8 K7). These data point out calcium-signaling as a key cellular target for viral infection and should stimulate further studies exploring new calcium-related therapeutic strategies.

Calcium Signaling↗
PubMed1991

Synthesis of the NS 2 nonstructural protein messenger RNA of influenza A viruses occurs in the absence of viral protein synthesis.

The NS 2 messenger RNA (mRNA) of several influenza A viruses was shown to be synthesized in primary transcription. Analysis of in vitro translation products of mRNAs from infected MDCK cells treated with cycloheximide indicated that the NS 2 mRNA in addition to the NS 1 mRNA was synthesized with PR/8, Udorn, and Aichi viruses. The findings indicated that the NS 1 mRNA of these viruses was able to be spliced into the NS 2 mRNA as a primary transcript without viral protein synthesis, although the extent of splicing varied among different virus strains.

Animals↗
PubMed1999

Subcellular localization of hepatitis C viral proteins in mammalian cells.

We determined the subcellular localization of hepatitis C viral (HCV) proteins as a first step towards the understanding of the functions of these proteins in the mammalian cell (CHO-K1). We used fluorescence emitted from green fluorescent protein (GFP)-fused to the viral proteins to determine the subcellular localization of the viral proteins. We found that most of the viral proteins were excluded from the nucleus. Core exhibited a globular pattern near the nucleus. NS2 was concentrated in the perinuclear space. NS4A accumulated in the ER and the Golgi regions. NS3 was detected in the nucleus as well as the cytoplasm, when it was expressed by itself. However, NS3 became restricted to the cytoplasm, when it was produced together with NS4A. NS4B showed a spot-like pattern throughout the cytoplasm. NS5A and NS5B were distributed throughout the cytoplasm in a mesh-like pattern. These results can provide a basis for further investigations into the functions of the HCV proteins.

Animals↗
PubMed2000

A dominant-negative herpesvirus protein inhibits intranuclear targeting of viral proteins: effects on DNA replication and late gene expression.

The d105 dominant-negative mutant form of the herpes simplex virus 1 (HSV-1) single-stranded DNA-binding protein, ICP8 (d105 ICP8), inhibits wild-type viral replication, and it blocks both viral DNA replication and late gene transcription, although to different degrees (M. Gao and D. M. Knipe, J. Virol. 65:2666-2675, 1991; Y. M. Chen and D. M. Knipe, Virology 221:281-290, 1996). We demonstrate here that this protein is also capable of preventing the formation of intranuclear prereplicative sites and replication compartments during HSV infection. We defined three patterns of ICP8 localization using indirect immunofluorescence staining of HSV-1-infected cells: large replication compartments, small compartments, and no specific intranuclear localization of ICP8. Cells that form large replication compartments replicate viral DNA and express late genes. Cells that form small replication compartments replicate viral DNA but do not express late genes, while cells without viral replication compartments are incapable of both DNA replication and late gene expression. The d105 ICP8 protein blocks formation of prereplicative sites and large replication compartments in 80% of infected cells and formation of large replication compartments in the remaining 20% of infected cells. The phenotype of d105 suggests a correlation between formation of large replication compartments and late gene expression and a role for intranuclear rearrangement of viral DNA and bound proteins in activation of late gene transcription. Thus, these results provide evidence for specialized machinery for late gene expression within replication compartments.

Animals↗
PubMed2003

Modulation of Borna disease virus phosphoprotein nuclear localization by the viral protein X encoded in the overlapping open reading frame.

Borna disease virus (BDV) is a nonsegmented, negative-strand RNA virus that belongs to the Mononegavirales order. Unlike other animal viruses in this order, BDV replicates and transcribes in the nucleus of infected cells. Therefore, regulation of the intracellular movement of virus components must be critical for accomplishing the BDV life cycle in mammalian cells. Previous studies have demonstrated that BDV proteins are prone to accumulate in the nucleus of cells transiently transfected with each expression plasmid of the viral proteins. In BDV infection, however, cytoplasmic distribution of the viral proteins is frequently found in cultured cells and animal brains. In this study, to understand the modulation of subcellular localization of BDV proteins, we investigated the intracellular localization of the viral phosphoprotein (P). Transient-transfection analysis with a cDNA clone corresponding to a bicistronic transcript that expresses both viral X and P revealed that P efficiently localizes in the cytoplasm only when BDV X is expressed in the cells. Furthermore, our analysis revealed that the direct binding between X and P is necessary for the cytoplasmic localization of the P. Interestingly, we showed that X is not detectably expressed in the BDV-infected cells in which P is predominantly found in the nucleus, with little or no signal in the cytoplasm. These observations suggested that BDV P can modulate their subcellular localization through binding to X and that BDV may regulate the expression ratio of each viral product in infected cells to control the intracellular movement of the viral protein complexes. The results presented here provide a new insight into the regulation of the intracellular movement of viral proteins of a unique, nonsegmented, negative-strand RNA virus.

Animals↗
PubMed1978

Simple method for preparation of specific antisera against viral proteins: rabbit antisera against equine infectious anemia virus proteins p26 and p16.

A simple method for preparation of highly specific antisera against equine infectious anemia virus proteins p26 and p16 is described. Viral proteins were separated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The motility of the viral proteins in the gel was compared with standards. Unstained portions of the slab gel were sliced into 5-mm bands, emulsified with Freund's complete adjuvant, and injected into rabbits to produce specific antisera.

Animals↗
PubMed2004

Quantification of infectious bursal disease viral proteins 2 and 3 in inactivated vaccines as an indicator of serological response and measure of potency.

Viral protein 2 and viral protein 3 (VP2 and VP3) were quantified in a series of inactivated infectious bursal disease oil emulsion vaccines using enzyme-linked immunosorbent assay, and the dependence of the serological response on vaccine antigen content was studied. Large differences in antigen content, up to 50-fold, were found between vaccines. Neutralizing antibody titres at 3 to 6 weeks after vaccination varied from 3 log2 to 16 log2. None of the vaccines induced an antibody titre equal to that of the reference serum used as an indicator of sufficient potency in the European Pharmacopoeia. Neutralizing antibody titres after vaccination correlated highly with the VP2 content of the vaccines. A significant correlation was also found between the VP3 content and the antibody response. Our data illustrate that the antigen content of inactivated infectious bursal disease vaccines is a reliable indicator of the protective serological response after vaccination, and consequently could be used as a measure of vaccine potency. This holds true for both VP2, the antigen that induces neutralizing antibodies, as well as for VP3, which does not induce neutralizing antibodies.

Animals↗
PubMed1991

Antibodies against dengue viral proteins in primary and secondary dengue hemorrhagic fever.

Antibodies against dengue viral proteins were demonstrated in sera from dengue-infected patients by polyacrylamide gel electrophoresis, Western blotting, and enzyme immunoassay. Primary dengue cases showed low titers of IgG class antibodies to envelope (E) proteins and two non-structural proteins, NS3 and NS5, in sera collected during the convalescent phase. Secondary dengue- infected patients always demonstrated IgG antibodies to E proteins in sera collected during the acute phase, and high titers of IgG antibodies to many other proteins, including NS1, NS3, NS5, and C proteins in sera collected during the convalescent phase. Appearance of antibodies to E, NS3, and NS5 could be detected within five days after the onset of fever. These three dengue viral proteins and their corresponding antibodies may be involved in the immunopathologic mechanism underlying this disease. For diagnostic purposes, identifying the non-structural proteins such as NS3 and NS5 may be the best means for early confirmation of the disease.

Acute Disease↗
PubMed2007

Virus-PLoc: a fusion classifier for predicting the subcellular localization of viral proteins within host and virus-infected cells.

Viruses can reproduce their progenies only within a host cell, and their actions depend both on its destructive tendencies toward a specific host cell and on environmental conditions. Therefore, knowledge of the subcellular localization of viral proteins in a host cell or virus-infected cell is very useful for in-depth studying of their functions and mechanisms as well as designing antiviral drugs. An analysis on the Swiss-Prot database (version 50.0, released on May 30, 2006) indicates that only 23.5% of viral protein entries are annotated for their subcellular locations in this regard. As for the gene ontology database, the corresponding percentage is 23.8%. Such a gap calls for the development of high throughput tools for timely annotating the localization of viral proteins within host and virus-infected cells. In this article, a predictor called "Virus-PLoc" has been developed that is featured by fusing many basic classifiers with each engineered according to the K-nearest neighbor rule. The overall jackknife success rate obtained by Virus-PLoc in identifying the subcellular compartments of viral proteins was 80% for a benchmark dataset in which none of proteins has more than 25% sequence identity to any other in a same location site. Virus-PLoc will be freely available as a web-server at http://202.120.37.186/bioinf/virus for the public usage. Furthermore, Virus-PLoc has been used to provide large-scale predictions of all viral protein entries in Swiss-Prot database that do not have subcellular location annotations or are annotated as being uncertain. The results thus obtained have been deposited in a downloadable file prepared with Microsoft Excel and named "Tab_Virus-PLoc.xls." This file is available at the same website and will be updated twice a year to include the new entries of viral proteins and reflect the continuous development of Virus-PLoc.

Cells↗
PubMed1996

Injury models of the vascular endothelium: apoptosis and loss of thromboresistance induced by a viral protein.

Endothelial injury caused by viruses usually involves viral replication or transformation. We report a novel mechanism of endothelial damage by a toxic viral protein. We have isolated a new retrovirus from hemangiosarcomas which appeared among layer hens. The isolated avian hemangiosarcoma virus (AHV) is capable of inducing hemangiomas in hens in-vivo and causes a cytopathic effect (CPE) and loss of thromboresistance in cultured bovine aortic endothelial cells (BAEC). These effects do not require viral replication and can be induced by purified AHV envelop glycoprotein (gp85). AHV causes CPE in BAEC through a typical programmed cell death (apoptosis). Quiescent G0/G1-BAEC are much more sensitive to AHV induced apoptosis than actively dividing cells. These experiments demonstrate the capacity of viral proteins to affect the integrity and functionality of vascular endothelial cells.

Animals↗
PubMed1997

Genetic dissection of interaction between poliovirus 3D polymerase and viral protein 3AB.

Poliovirus RNA-dependent RNA polymerase 3D and viral protein 3AB are both thought to be required for the initiation of RNA synthesis. These two proteins physically associate with each other and with viral RNA replication complexes found on virus-induced membranes in infected cells. An understanding of the interface between 3D and 3AB would provide a first step in visualizing the architecture of the multiprotein complex that is assembled during poliovirus infection to replicate and package the viral RNA genome. The identification of mutations in 3D that diminish 3D-3AB interactions without affecting other functions of 3D polymerase is needed to study the function of the 3D-3AB interaction in infected cells. We describe the use of the yeast two-hybrid system to isolate and characterize mutations in 3D polymerase that cause it to interact less efficiently with 3AB than wild-type polymerase. One mutation, a substitution of leucine for valine at position 391 (V391L), resulted in a 3AB-specific interaction defect in the two-hybrid system, causing a reduction in the interaction of 3D polymerase with 3AB but not with another viral protein or a host protein tested. In vitro, purified 3D-V391L polymerase bound to membrane-associated 3AB with reduced affinity. Poliovirus that contained the 3D-V391L mutation was temperature sensitive, displaying a pronounced conditional defect in RNA synthesis. We conclude that interaction between 3AB and 3D or 3D-containing polypeptides plays a role in RNA synthesis during poliovirus infection.

Alleles↗
PubMed1993

Dynamics of mitotic activity and expression of viral proteins gp51 and p24 of bovine leukemia virus producing cells.

The dynamics of expression of viral proteins gp51 and p24, virus particle production and mitotic activity of a highly productive bovine leukemia virus clone of the fetal lamb kidney (FLK) cell line were studied. The period of the highest protein production (20-44 h after incubation) was established by the indirect immunofluorescence method using specific monoclonal antibodies. It was followed by a complete formation of the cell monolayer and the most intensive period of the mitotic activity determined by the 3H-thymidine labeling method. After the active synthesis of viral protein, the formation of mature viral particles and their shedding in the intercellular spaces was established electron-microscopically and by the syncytia induction test. A similar comparative study was carried out with a BLV producing short-term lymphocyte culture (STLC).

Animals↗
PubMed1991

Virucidal activity and viral protein modification by myeloperoxidase: a candidate for defense factor of human polymorphonuclear leukocytes against influenza virus infection.

Influenza virus (IFV) was inactivated by treatment with degranulated fluid (DF) or myeloperoxidase (MPO) from human polymorphonuclear leukocytes in the presence of H2O2. Hemagglutinin and neuraminidase activities of the virus were also reduced by DF treatment. In addition, treatment with DF or MPO in the presence of H2O2 resulted in delayed migration of viral proteins in SDS-PAGE, indicating extensively modified viral proteins. Parallel with this aberrant migration, the radioactivity of each protein band on SDS-PAGE using [35S]methionine-labeled IFV was greatly reduced. Moreover, some of the modified viral protein did not migrate. A small amount of acid-soluble degraded viral peptide was also generated. The modification of the proteins was exhibited in all major viral proteins, including the inner proteins in the envelope. These results suggest that inactivation of IFV and protein modification by DF is due to MPO present in DF.

Cell Degranulation↗