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At least 1,207 records · Page 67Linked to original sources
PubMed2003

Interaction of Borrelia burgdorferi sensu lato with Epstein-Barr virus in lymphoblastoid cells.

Since the possibility of interruption of latent EBV infection has been suggested by the induction of the lytic virus cycle with chemical substances, other viruses, and by immunosuppression, we hypothesized that the same effect might happen in B. burgdorferi sensu lato infection as happens in Lyme disease patients with positive serology for both agents. We have observed EBV replication in lymphoblastoid cells after superinfection with B. garinii and B. afzelii strains after 1 and 4 h of their interaction. We found that viral and borrelial antigens persisted in the lymphoblasts for 3 and 4 days. Morphological and functional transformation of both agents facilitate their transfer to daughter cells. Association with lymphoblasts and internalization of B. garinii by tube phagocytosis increased replication of viruses more successfully than B. afzelii and chemical inductors. Demonstration of such findings must be interpreted cautiously, but may prove a mixed borrelial and viral cause of severe neurological disease.

Borrelia burgdorferi↗
PubMed1990

Studies of cloned simian immunodeficiency virus-specific T lymphocytes. gag-specific cytotoxic T lymphocytes exhibit a restricted epitope specificity.

CD8+ CTL inhibit the replication of HIV and simian immunodeficiency virus of macaques (SIVmac) in PBL and, therefore, are likely to play an important role in containing the spread of the AIDS virus in infected individuals. We have generated a series of gag-specific lytic T lymphocyte clones from PBL: of an SIVmac-infected rhesus monkey. These T cell clones are CD3+CD8+ and are MHC class I-restricted in their target specificity. They are, therefore, CTL. Interestingly, all gag-specific CTL clones, as well as the gag-specific lytic activity of PBL of this monkey, demonstrated specificity for a single 25 amino acid fragment of the SIVmac gag protein. Moreover, they were restricted in their lytic function by a single MHC class I allele. These findings illustrate a powerful method for cloning AIDS virus-specific T lymphocytes and demonstrate a remarkably restricted epitope specificity of this AIDS virus-specific CTL response.

Animals↗
PubMed1998

Exploring brain circuitry with neurotropic viruses: new horizons in neuroanatomy.

There have been substantial advances in methods for defining connections among neurons over the past quarter century. However, most tracers have been limited in their ability to define populations of functionally related neurons that contribute to a multisynaptic circuit because they are not transported across synapses. As a result, the large body of literature that has employed these tracers has established regional associations between regions that must be further explored with electron microscopy and electrophysiological methods to define the synaptic relations among constituent neurons. Recently, neurotropic alpha herpesviruses have been used to visualize ensembles of neurons that contribute to polysynaptic networks. These pathogens invade permissive cells, replicate, and pass transynaptically to infect other neurons. In effect, the viruses become self-amplifying tracers whose natural tropism and invasiveness define populations of functionally related neurons. The recent increase in the use of this experimental approach has emerged from advances in our understanding of the life cycle of these viruses and the resulting evidence in support of specific transynaptic passage of progeny virus rather than infection by lytic release into the extracellular space. This article reviews the advances that have made this a viable experimental approach and considers ways in which this method has been creatively used to illuminate aspects of nervous system circuit organization that could not be defined with conventional tracers.

Animals↗
PubMed2005

The genome of S-PM2, a "photosynthetic" T4-type bacteriophage that infects marine Synechococcus strains.

Bacteriophage S-PM2 infects several strains of the abundant and ecologically important marine cyanobacterium Synechococcus. A large lytic phage with an isometric icosahedral head, S-PM2 has a contractile tail and by this criterion is classified as a myovirus (1). The linear, circularly permuted, 196,280-bp double-stranded DNA genome of S-PM2 contains 37.8% G+C residues. It encodes 239 open reading frames (ORFs) and 25 tRNAs. Of these ORFs, 19 appear to encode proteins associated with the cell envelope, including a putative S-layer-associated protein. Twenty additional S-PM2 ORFs have homologues in the genomes of their cyanobacterial hosts. There is a group I self-splicing intron within the gene encoding the D1 protein. A total of 40 ORFs, organized into discrete clusters, encode homologues of T4 proteins involved in virion morphogenesis, nucleotide metabolism, gene regulation, and DNA replication and repair. The S-PM2 genome encodes a few surprisingly large (e.g., 3,779 amino acids) ORFs of unknown function. Our analysis of the S-PM2 genome suggests that many of the unknown S-PM2 functions may be involved in the adaptation of the metabolism of the host cell to the requirements of phage infection. This hypothesis originates from the identification of multiple phage-mediated modifications of the host's photosynthetic apparatus that appear to be essential for maintaining energy production during the lytic cycle.

Bacteriophages↗
PubMed1998

Inhibition of human immunodeficiency type 1 virus replication in monocytic U-937 cells by superinfection with Chlamydia trachomatis.

The aim of this study was to investigate the effects of infection of monocytic cells with both the human immunodeficiency type 1 virus (HIV-1) and Chlamydia trachomatis on the replication of each pathogen. U-937 cells, chronically infected with HIV-1 (strain LaVLai), either induced to differentiate into immature macrophage-like cells by 32 pM 12-O-tetradecanol phorbol-13-acetate or uninduced, were superinfected with C. trachomatis serovar L2. Both HIV-1 infection and differentiation rendered the U-937 cells highly susceptible to C. trachomatis lytic infection. Differentiation and superinfection of HIV-1-infected cells with C. trachomatis both affected cell viability and reduced viral production in vitro. RT activity was one tenth the original value after differentiation of HIV-1-infected cells, one twentieth the original value after superinfection with C. trachomatis, and one hundredth the original value after differentiation and superinfection with C. trachomatis.

Antibiosis↗
PubMed1991

Host range specificity of polyomavirus EC mutants in mouse embryonal carcinoma and embryonal stem cells and preimplantation embryos.

New polyomavirus mutants (PyEC-C) selected on LT1 cells and exhibiting a strong cytopathic effect in all embryonal carcinoma (EC) cell lines tested have been isolated. They were derived by a sequence duplication event from a new multiadapted mutant isolated in PCC4 cells. A quantitative analysis of viral DNA replication and transcription in 3T6 and EC cell lines was performed to compare PyEC-C mutants and PyEC mutants previously isolated on F9 or PCC4 cell lines. Analysis of the results indicated that PyEC-C mutants were more efficient in all EC cell lines tested than all other PyEC mutants; on the contrary, they were less adapted to 3T6 cells than wild-type polyomavirus. In both 3T6 and EC cells, uncoupling between early transcription and viral DNA replication was observed; different viruses were shown to replicate with the same efficiency, while their levels of early transcripts differed by two orders of magnitude. Attempts to correlate the genome structure of the mutants with their biological properties indicate that duplication of protein-binding sequences is not the only event responsible for their phenotype. PyEC mutants were also analyzed with respect to their interactions with early mouse embryos and embryonal stem (ES) cell lines derived from the inner cell mass of blastocysts. They showed different degrees of expression in ES cells and preimplantation embryos. ES cells were most efficiently infected and lysed by mutants which exhibit both a multiadapted and a lytic phenotype in EC cells. Preimplantation embryos were not permissive to any PyEC mutants. However, EC-multiadapted mutants were infectious in blastocysts after two days of in vitro culture.

Animals↗
PubMed1994

Tacaribe virus gene expression in cytopathic and non-cytopathic infections.

Tacaribe virus (TV) replication was compared in Vero cells infected under conditions leading either to cell death (c.p.e.(+) infection) or to the establishment of persistence (c.p.e.(-) infection). To this end, two virus preparations were employed: one containing a ratio of standard (plaque-forming) viruses to interfering particles (IP) that would induce a distinct lytic response in Vero cells infected at multiplicities giving synchronous infection and another virus stock enriched in IP that would block the cell-killing potential of the cytolytic virus stock. The following results were obtained: (1) No qualitative differences were observed in the species of intracellular viral RNAs in the lytic infection in comparison with infections leading to persistence or during the early stages of persistence. (2) Levels of viral RNAs were severely reduced when the cells were infected with IP in addition to standard viruses, the RNA accumulation being inversely proportional to the ratio of IP to standard viruses used in the infections. (3) Accumulation of the three measurable mRNAs (those corresponding to the glycoprotein precursor [GPC], to the nucleoprotein [N], and to the p11Z protein) ended earlier in the c.p.e.(-) infections (around 18 hr p.i.) than in the c.p.e.(+) infection (45-68 hr p.i.). (4) The rates of synthesis of the GPC, N, and p11Z proteins were largely determined in both the c.p.e.(+) and c.p.e.(-) infections by the amounts of their corresponding mRNAs. (5) The kinetics of accumulation of the S genomes and also the ratios of the S genome to S antigenome were similar in the different infections (accumulation ending at 45-68 hr p.i.). (6) L genome accumulation proceeded for longer time (until 92 hr p.i.) in the c.p.e.(+) infection than in the c.p.e.(-) infections. In the latter accumulation ended at around 45 hr p.i. Until this time ratios of L genome to L antigenome were similar in the different infections. It is concluded that IP affect virus mRNA synthesis early after infection reducing in this way the rate of viral protein synthesis. Low levels of viral proteins might then limit virus replication. In addition, the results support the idea that in TV infections transcription and replication are independently regulated. The implications of these results with regards to the nature and mode of action of TV IP are discussed.

Animals↗
PubMed1987

Repair of single-stranded loops in heteroduplex DNA transfected into mammalian cells.

Repair of heteroduplex DNA, generated between two interacting DNA molecules during homologous recombination, has been implicated as a contributing factor in the process of gene conversion. To assess patterns of heteroduplex repair in mammalian cells, we constructed 13 different heteroduplexes from simian virus 40 wild-type and deletion mutant DNAs. Each heteroduplex contained one or multiple single-stranded loops in the intron of the gene for large tumor antigen, which is not essential during lytic infection. After transfection into cultured monkey cells, cellular repair was evaluated by restriction analysis of the amplified viral progeny from 1123 individual plaques, each representing the clonal expansion of a single repair event. Single-stranded loops were corrected prior to replication with an overall efficiency of 90%. At the position of a loop, one of the two heteroduplex strands served as a template for accurate repair 98% of the time. Repair of single-stranded loops was biased nearly 2 to 1 in favor of the strand without the loop. The efficiency, accuracy, and strand bias of repair were unaffected by loop size within the tested range, which was 25-247 nucleotides. The excision tract associated with repair of single-stranded loops rarely exceeds 200-400 nucleotides in length.

Cell Line↗
PubMed1987

Expression of a cellular gene cloned in herpes simplex virus: rabbit beta-globin is regulated as an early viral gene in infected fibroblasts.

We constructed nondefective herpes simplex virus type 1 recombinants bearing the intact rabbit beta-globin gene inserted into the viral gene for thymidine kinase to study the expression of a cellular gene when it is present in the viral genome during lytic viral infections. The globin promoter was activated to high levels during productive infection of Vero cells, giving rise to properly spliced and processed cytoplasmic globin transcripts. Expression of globin RNA occurred with early kinetics, was not affected by blocking viral DNA replication, and was strongly inhibited by preventing viral immediate-early protein synthesis with cycloheximide. These results support the hypothesis that temporal control of herpes simplex virus early gene expression is accomplished by mechanisms that are not restricted to viral promoters. In addition, these data show that a cellular transcript can be correctly processed and can accumulate to high levels during viral infection; this indicates that the mechanisms of virally induced shutoff of host RNA accumulation and degradation of host mRNAs do not depend on sequence-specific differentiation between host and viral RNAs. These findings also suggest that herpesviruses have considerable potential as high-capacity gene transfer vectors for a variety of applications.

Animals↗
PubMed2000

Identification of the pseudorabies virus promoter required for latency-associated transcript gene expression in the natural host.

Expression of the latency-associated transcript (LAT) gene is a hallmark of alphaherpesvirus latency, and yet its control and function remain an enigma. Resolution of this problem will require verification and subsequent elimination or disabling of elements regulating LAT gene transcription so that the influence of the resultant RNA can be evaluated. Toward this end, we generated a novel pseudorabies virus (PrV) recombinant in which a 282-bp region containing the LAP1 (first latency-active promoter) consensus sequence was replaced by a reporter cassette. Despite this substitution, replication of the recombinant was comparable to that of the parental and rescuant viruses both in cultured mammalian cells and in the natural host, swine. Furthermore, production of the LAT gene-associated 2.0- and 8.0-kb RNAs during an in vitro lytic infection of cultured neuronal cells was unaffected. However, the otherwise constitutively produced and processed 8.4-kb LAT was not detected in porcine trigeminal ganglia latently infected with this novel recombinant, although the viral genome was shown to be present. Therefore, LAP1 is apparently the basal promoter for PrV LAT gene expression during viral latency but is not required for such activity during an in vitro lytic infection of neuronal cells. More importantly, the ability of PrV to persist in a latent state in the absence of LAT suggests that other factors are responsible for this event in the natural host.

Animals↗
PubMed2004

The reading frame BPLF1 of Epstein-Barr virus: a homologue of herpes simplex virus protein VP16.

The open reading frame BPLF1 of Epstein-Barr virus (EBV) shows homology to the Herpes simplex virus 1 (HSV1) protein VP16. This protein is a structural tegument component playing a pivotal role for HSV replication as trans-activator of viral immediate-early genes. An EBV gene with a comparable function has not been described so far. However, computer analysis indicated that BPLF1 may be a tegument protein homologous to VP16. This is the first report on the characterisation of the BPLF1 gene, its transcription, and expression of its gene product in vitro and in vivo. Using RT-PCR and Northern blot assays we demonstrated that the BPLF1 gene belongs to the class of late lytic cycle genes of EBV. Besides a full length transcript of 9.5 kb also a polyadenylated transcript of approximately 3 kb is synthesised. However, no consensus splice sites could be identified. Northern blot experiments using partially overlapping probes and sequencing of a BPLF1-specific cDNA revealed 1,550 nucleotides of the BPLF1 transcript, collinear in sequence with the viral genome from position 64547 to 66097. A recombinant Western blot assay detected BPLF1-specific antibodies in seropositive individuals, in particular in cases with elevated viral replication like infectious mononucleosis, chronic active infection, and nasopharyngeal carcinoma. This demonstrated expression of the BPLF1 protein in vivo. Thus, experimental data and computer analysis strongly support the hypothesis of BPLF1 being a tegument protein of the EBV homologous to VP16 of HSV1 and ORF22 of Varicella zoster virus.

Animals↗
PubMed1990

Interactions between SV40 T antigen and DNA polymerase alpha.

Simian virus 40 large T antigen is the only viral protein required for SV40 DNA synthesis in vivo and in vitro. This complex protein recruits the cellular DNA replication apparatus to the SV40 origin and provides a good model for the initiation of cellular DNA replication. The interaction between SV40 large T antigen (TAg) and DNA polymerase alpha has been shown previously to be inhibited by murine p53, the nuclear protein product of a cellular anti-oncogene. The murine p53 protein will inhibit SV40 replication both in vivo and in vitro. Using monoclonal antibodies to TAg, p53, and polymerase alpha, we developed immunoassays to measure the complexes formed between TAg and polymerase alpha and between TAg and p53. The assays allowed us to detect the TAg-polymerase alpha and TAg-p53 complexes in lytically infected and transformed cells. The amount of TAg complexed to p53 was far lower in infected cells than in transformed cells. We used a large range of monoclonal antibodies to different sites on T antigen and found that antibodies that inhibited the formation of the TAg-polymerase alpha complex also inhibited the formation of the TAg-p53 complex. Finally, we found that the tsA58 and 5080 point mutations in TAg, previously shown to inhibit the binding of TAg to p53, also inhibit its binding to polymerase alpha. Together these results emphasize the specificity and functional importance of the TAg-polymerase alpha complex. The disruption of this interaction by the cellular anti-oncogene p53 provides an interesting model for the normal action of p53 and the effects of its removal on the regulation of cellular DNA synthesis.

Animals↗
PubMed1994

Evasion of host immune responses by tumours and viruses.

Viruses and tumours use various mechanisms to avoid immune surveillance. Oncogenic viruses have achieved a balance with the immune system through evolutionary time to ensure long-term persistence. Mutations that promote escape mechanisms favouring tumour growth to the detriment of host survival through reproductive age offer no selective advantage and will not generally be maintained in the viral genome that persists in nature. Conventional (non-oncogenic) and tumour viruses interact with various immune mediators and T cells in different ways. Oncogenic viruses cannot operate solely in the context of a lytic cycle, though this may be characteristic of the initial phase of infection that is limited by the acute immune response. Some oncogenic viruses interact with normal cellular growth control and signalling mechanisms. Synthesis of key viral proteins may be tightly controlled in replicating cells that are subject to T cell surveillance, such as basal epithelia, while productive infection occurs in non-proliferating progeny that are lost under normal physiological conditions, such as desquamating epithelia. Tumorigenesis may be an aberrant consequence of the molecular mechanisms needed to maintain this pattern of viral growth regulation in the context of the cell cycle. Vaccines designed to limit the acute phase of infection with cell-free oncogenic viruses should be as effective as those for conventional viruses.

Adenoviruses, Human↗
PubMed1992

Control of adenovirus major late gene expression at multiple levels.

Most late adenovirus (Ad) proteins are translated from mRNAs originating from the so-called major late transcription unit (MLTU). These mRNAs are grouped into five families (designated L1 to L5), where each family consists of mRNAs that have co-terminal 3' ends. We have used mutant and wild-type Ad infections to characterize levels at which major late gene expression is regulated. Our results suggest the existence of a novel intermediate stage during a lytic infection where mRNAs from regions L1 and L4 are selectively overexpressed compared to the L2, L3, and L5 mRNAs. Our data suggest that this RNA phenotype reflects the activity of the MLTU at a transient stage immediately following initiation of viral DNA replication. Early during an Ad infection only mRNA from region L1 accumulate. To efficiently accumulate mRNA from regions L1 and L5 both viral DNA replication and late protein synthesis were required. To allow for only viral DNA replication resulted in an extensive premature transcription termination and a preferential mRNA accumulation from regions L1 and L4. The surprising production of L4 mRNA under these conditions was not due to the activation of a novel r-strand promoter located in the vicinity of region L4 or due to a control at the level of RNA transport or stability. Instead our results indicate that in the absence of efficient late protein synthesis 3' end formation occurs preferentially at the L1 and L4 poly(A) addition sites.

Adenoviridae↗
PubMed2005

Early and sustained expression of latent and host modulating genes in coordinated transcriptional program of KSHV productive primary infection of human primary endothelial cells.

Coordinated expression of viral genes in primary infection is essential for successful infection of host cells. We examined the expression profiles of Kaposi's sarcoma-associated herpesvirus (KSHV) transcripts in productive primary infection of primary human umbilical vein endothelial cells by whole-genome reverse-transcription real-time quantitative PCR. The latent transcripts were expressed early and sustained at high levels throughout the infection while the lytic transcripts were expressed in the order of immediate early, early, and lytic transcripts, all of which culminated before the production of infectious virions. Significantly, transcripts encoding genes with host modulating functions, including mitogenic and cell cycle-regulatory, immune-modulating, and anti-apoptotic genes, were expressed before those encoding viral structure and replication genes, and sustained at high levels throughout the infection, suggesting KSHV manipulation of host environment to facilitate infection. The KSHV transcriptional program in a primary infection defined in this study should provide a basis for further investigation of virus-cell interactions.

Apoptosis↗
PubMed1997

Bacteriophages of Streptococcus pneumoniae: a molecular approach.

We have characterized four families of pneumococcal phages with remarkable morphologic and physiological differences. Dp-1 and Cp-1 are lytic phages, whereas HB-3 and EJ-1 are temperate phages. Interestingly, Cp-1 and HB-3 have a terminal protein covalently linked to the 5' ends of their lineal DNAs. In the case of Dp-1, we have found that the choline residues of the teichoic acid were essential components of the phage receptors. We have also developed a transfection system using mature DNAs from Dp-4 and Cp-1. In the later case, the transfecting activity of the DNA was destroyed by treatment with proteolytic enzymes, a feature also shared by the genomes of several small Bacillus phages. DNA replication was investigated in the case of Dp-4 and Cp-1 phages. The terminal protein linked to Cp-1 DNA plays a key role in the peculiar mechanism of DNA replication that has been coined as protein-priming. Recently, the linear 19,345-bp double-stranded DNA of Cp-1 has been completely sequenced, several of its gene products have been analyzed, and a complete transcriptional map has been ellaborated. Most of the pneumococcal lysins exhibit an absolute dependence of the presence of choline in the cell wall substrate for activity, and phage lysis requires, as reported for other systems, the action of a second phage-encoded protein, the holin, which presumably forms some kind of lesion in the membrane. The two lytic gene cassettes, from EJ-1 and Cp-1 phages, have been cloned and expressed in heterologous and homologous systems. The finding that some lysogenic strains of Streptococcus pneumoniae harbor phage remnants has provided important clues on the interchanges between phage and bacteria and supports the view of the chimeric origin of phages.

DNA Replication↗