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A method for the re-isolation of an autonomously replicating plasmid from Aspergillus transformants.

An autonomously replicating plasmid is expected to increase the frequency of Aspergillus transformation. To construct this type of plasmid, we developed a rapid method of re-isolating autonomously replicating plasmids from Aspergillus transformants. Transformants grown in MM medium under selective pressure for 1-2 days were converted to protoplasts with a cell wall lytic enzyme (e.g. Yatalase). The protoplasts were lysed with phenol/chloroform followed by precipitation with ethanol. The total DNA was treated with RNaseA, re-precipitated with PEG, and then used to transform E. coli. These re-isolated plasmids were mainly the plasmid monomer.

Aspergillus↗

Effect of point mutations in the N terminus of the lentivirus lytic peptide-1 sequence of human immunodeficiency virus type 1 transmembrane protein gp41 on Env stability.

To understand the role of the lentivirus lytic peptide-1 region of the human immunodeficiency virus type 1 transmembrane glycoprotein (gp) 41 in viral infection, we examined the effects on virus replication of single amino acid deletions spanning this region in an infectious provirus of the HXB2 strain. Among the mutants analyzed, only the deletion of one of the two adjacent valine residues located at positions 832 and 833 (termed the Delta 833 mutant for simplicity) greatly reduced the steady-state, cell-associated levels of the Env precursor and gp120, as opposed to the wild-type virus. The altered Env phenotype resulted in severely impaired virus infectivity and gp120 incorporation into this mutant virion. Analyses of additional mutants with deletions at Ile-830, Ala-836, and Ile-840 demonstrated that the Delta 830 mutant exhibited the most significant inhibitory effect on Env steady-state expression. These results indicate that the N terminus of the lentivirus lytic peptide-1 region is critical for Env steady-state expression. Among the mutant viruses encoding Env proteins in which residues Val-832 and Val-833 were individually substituted by nonconserved amino acids Ala, Ser, or Pro, which were expected to disrupt the alpha-helical structure in the increasingly severe manner of Pro > Ser > Ala, only the 833P mutant exhibited significantly reduced steady-state Env expression. Pulse labeling and pulse-chase studies demonstrated that the Delta 830, Delta 833, and 833P mutants of Env proteins degraded more rapidly in a time-dependent manner after biosynthesis than did the wild-type Env. The results indicate that residue 830 and 833 mutations are likely to induce a conformational change in Env that targets the mutant protein for cellular degradation. Our study has implications about the structural determinants located at the N terminus of the lentivirus lytic peptide-1 sequence of gp41 that affect the fate of Env in virus-infected cells.

Amino Acid Sequence↗

Lytic cycle of Toxoplasma gondii.

Toxoplasma gondii is an obligate intracellular pathogen within the phylum Apicomplexa. This protozoan parasite is one of the most widespread, with a broad host range including many birds and mammals and a geographic range that is nearly worldwide. While infection of healthy adults is usually relatively mild, serious disease can result in utero or when the host is immunocompromised. This sophisticated eukaryote has many specialized features that make it well suited to its intracellular lifestyle. In this review, we describe the current knowledge of how the asexual tachyzoite stage of Toxoplasma attaches to, invades, replicates in, and exits the host cell. Since this process is closely analogous to the way in which viruses reproduce, we refer to it as the Toxoplasma "lytic cycle."

Animals↗

Frequency of CD8(+) T lymphocytes specific for lytic and latent antigens of Epstein-Barr virus in healthy virus carriers.

We investigated CD8(+) T cell frequencies of five different Epstein-Barr virus-specific cytotoxic T lymphocyte epitopes located within proteins of the replicative cycle and the latent state in healthy long-term virus carriers with IFN-gamma enzyme-linked immunospot assay. Frequencies of the HLA-A3-restricted epitope RVRAYTYSK (RVR) whose minimal length was mapped in this study to amino acid position 148-156 of the immediate-early protein BRLF1 were compared with those of a further known HLA-A3-restricted epitope within EBNA3A, RLRAEAQVK (RLR). Determination of frequencies of CD8(+) T lymphocytes directed against lytic antigen epitope RVR revealed that only one of eight donors recognized this epitope. Frequency was calculated to be 65 RVR-specific CD8(+) T lymphocytes per 10(6) PBMC. None of the HLA-A3-positive donors exhibited IFN-gamma release after antigenic stimulation with the EBNA3A-specific peptide epitope RLR. Furthermore, we chose three known HLA-B8-restricted epitopes, RAKFKQLL (RAK), FLRGRAYGL (FLR), and QAKWRLQTL (QAK), of the lytic protein BZLF1 and the latent protein EBNA3A. Examination of eight HLA-B8-positive virus carriers revealed that the BZLF1-specific epitope RAK was recognized by all donors with a median frequency of 233 RAK-specific CD8(+) T lymphocytes per 10(6) PBMC. Only 50% of these donors reacted against EBNA3A-specific epitope FLR and a minority (25%) reacted against EBNA3A-specific epitope QAK.

CD8-Positive T-Lymphocytes↗

Role of the host cell in persistent viral infection: coevolution of L cells and reovoirus during persistent infection.

Mutant L cells, designated LR cells, were isolated after "curing" a persistently infected cell line (L/C) with antireovirus serum. The LR cells were shown to be virus-free; no reovirus was detectable by infectious center assays, plaque assays, presence of viral proteins, presence of viral dsRNA and immunofluorescence studies. Persistent infections were readily established n LR cells following infection with either cloned, low passage wild-type reovirus or cloned, low passage reovirus isolated from carrier cultures. Reovirus isolated from carrier cultures, however, grew much better than wild-type reovirus in LR cells and showed complete dominance over wild-type reovirus in coinfection experiments. Infection of LR cells with wild-type reovirus resulted in a low-level persistent infection with inefficient viral replication; these mutant L cells were partially resistant to infection with wild-type reovirus. In contrast, infection of the mutant L cells with virus isolated from the persistently infected cells resulted in a persistent infection accompanied with efficient viral replication. Infection of the original L cells with either wild-type reovirus or reovirus isolated from the persistently infected cells resulted in a lytic infection with no surviving cells. Thus the host cell plays a crucial role in the maintenance of persistent reovirus infection. Our results show that there is a coevolution of both mutant L cells and mutant reovirus during persistent infection.

Animals↗

Armed therapeutic viruses: strategies and challenges to arming oncolytic viruses with therapeutic genes.

Oncolytic viruses are attractive therapeutics for cancer because they selectively amplify, through replication and spread, the input dose of virus in the target tumor. To date, clinical trials have demonstrated marked safety but have not realized their theoretical efficacy potential. In this review, we consider the potential of armed therapeutic viruses, whose lytic potential is enhanced by genetically engineered therapeutic transgene expression from the virus, as potential vehicles to increase the potency of these agents. Several classes of therapeutic genes are outlined, and potential synergies and hurdles to their delivery from replicating viruses are discussed.

Animals↗

Interactions between a herpes simplex virus regulatory protein and cellular mRNA processing pathways.

The herpes simplex virus type 1 (HSV-1) immediate-early regulatory protein ICP27 performs essential functions during viral lytic infection. Studies with viral mutants have demonstrated that ICP27 affects the shutoff of host protein synthesis, HSV-1 DNA replication, and the expression of viral early and late genes. Mounting evidence has been presented to demonstrate that ICP27 functions predominantly at the posttranscriptional level by affecting mRNA processing. That is, ICP27 alters poly(A) site usage, impairs host cell splicing, and facilitates the export of viral intronless mRNAs. These diverse effects occur by the interaction of ICP27 with viral and host proteins and by binding RNA. To define the precise mechanisms by which ICP27 affects RNA processing pathways, it is necessary to identify all of the molecular interactions of ICP27 in vivo and to determine the functional significance of these interactions. In vivo approaches will be emphasized here. Protein-protein interactions have been analyzed by coimmunoprecipitation studies, followed by immunoblotting to confirm the identity of coprecipitating proteins. Indirect immunofluorescence staining has been performed on cells treated with RNA polymerase II inhibitors to determine the intracellular distribution of ICP27 related to its RNA export function. Finally, in vivo UV irradiation has been used to covalently cross-link ICP27 to mRNAs in direct contact. This was followed with procedures to isolate and analyze the protein-RNA complexes. These studies have revealed several splicing complex proteins with which ICP27 interacts and have identified a number of intronless RNA transcripts to which ICP27 binds in the nucleus and cytoplasm in its role in RNA transport.

Amino Acid Sequence↗

Characterization of human metapneumovirus infection of myeloid dendritic cells.

Recent in vivo studies suggest that hMPV is a poor inducer of inflammatory cytokines and that clinical symptoms may not be related to immune-mediated pathogenesis as it has been proposed for respiratory syncytial virus (RSV) and human parainfluenza 3 (HPF3). Dendritic cells (DCs) are specialized antigen presenting cells, and very effective at inducing specific CTLs after encountering invading viruses. Interactions of hMPV with DCs have not been characterized. We hypothesized that the relatively mild inflammatory responses observed in vivo after hMPV infection might be at least in part due to hMPV's poor ability to stimulate and activate DCs. hMPV actively infected immature monocyte-derived CD11c+/HLA-DR+ DCs. However, in contrast to RSV or HPF3, hMPV caused no gross cytopathic effects such as syncytia, lytic infection, or massive apoptosis. DCs exposed to hMPV show no cytopathic effects under tissue culture conditions permissive for viral replication. The surface maturation markers CD83 and CD86 were not significantly up-regulated in infected DCs as compared to uninfected controls, while expression of CD80 appeared increased. Stimulation of hMPV-infected DCs with LPS resulted in the enhanced expression of all these surface markers indicating that hMPV is not generally suppressing DC maturation. Overall, cytokine expression remained low. These results indicate that hMPV does not induce effective DC maturation in vitro and suggest that the weak stimulation of DCs may account for the overall low immunogenicity of this virus observed in vivo.

Cell Differentiation↗

Structure, synthesis, and activity of dermaseptin b, a novel vertebrate defensive peptide from frog skin: relationship with adenoregulin.

A novel antimicrobial peptide, designated dermaseptin b, was isolated from the skin of the arboreal frog Phyllomedusa bicolor. This 27-residue peptide amide is basic, containing 3 lysine residues that punctuate an alternating hydrophobic and hydrophilic sequence. In helix-inducing solvent, dermaseptin b adopts an amphipathic alpha-helical conformation that most closely resembles class L amphipathic helixes, with all lysine residues on the polar face of the helix. The peptide exhibits growth inhibition activity in vitro against a broad spectrum of pathogenic microorganisms including yeast and bacteria as well as various filamentous fungi that are responsible for severe opportunistic infections accompanying acquired immunodeficiency syndrome and the use of immunosuppressive agents. Maximized pairwise sequence alignment of dermaseptin b and dermaseptin s, a 34-residue antimicrobial peptide previously isolated from Phyllomedusa sauvagii, reveals 81% amino acid identity. No other significant similarity was found between dermaseptin b and any prokaryotic or eukaryotic protein, but similarity was found with adenoregulin (38% amino acid postional identity), a 33-residue peptide that enhances binding of agonists to the A1 adenosine receptor. The synthetic replicates of dermaseptin b and adenoregulin displayed similar but nonidentical spectra of antimicrobial activity, and both peptides were devoid of lytic effect on mammalian cells. Accordingly, the observation that adenoregulin enhances binding of agonists to the adenosine receptor may in fact be a consequence of its ability to alter the structure of biological membranes and to produce signal transduction via interactions with the lipid bilayer, bypassing cell surface receptor interactions.

Amino Acid Sequence↗

Genomic sequence of C1, the first streptococcal phage.

C(1), a lytic bacteriophage infecting group C streptococci, is one of the earliest-isolated phages, and the method of bacterial classification known as phage typing was defined by using this bacteriophage. We present for the first time a detailed analysis of this phage by use of electron microscopy, protein profiling, and complete nucleotide sequencing. This virus belongs to the Podoviridae family of phages, all of which are characterized by short, noncontractile tails. The C(1) genome consists of a linear double-stranded DNA molecule of 16,687 nucleotides with 143-bp inverted terminal repeats. We have assigned functions to 9 of 20 putative open reading frames based on experimental substantiation or bioinformatic analysis. Their products include DNA polymerase, holin, lysin, major capsid, head-tail connector, neck appendage, and major tail proteins. Additionally, we found one intron belonging to the HNH endonuclease family interrupting the apparent lysin gene, suggesting a potential splicing event yielding a functional lytic enzyme. Examination of the C(1) DNA polymerase suggests that this phage utilizes a protein-primed mechanism of replication, which is prominent in the phi29-like members of Podoviridae. Consistent with this evidence, we experimentally determined that terminal proteins are covalently attached to both 5' termini, despite the fact that no homology to known terminal proteins could be elucidated in any of our open reading frames. Likewise, comparative genomics revealed no close evolutionary matches, suggesting that the C(1) bacteriophage is a unique member of the Podoviridae.

Animals↗

Functional interactions between herpes simplex virus immediate-early proteins during infection: gene expression as a consequence of ICP27 and different domains of ICP4.

Two of the five immediate-early gene products, ICP4 and ICP27, expressed by herpes simplex virus type 1 have profound effects on viral gene expression and are absolutely essential for virus replication. Functional interactions between ICP4 and ICP27 may contribute to establishing the program of viral gene expression that ensues during lytic infection. To evaluate this possibility, viral mutants simultaneously deleted for ICP27 and defined functional domains of ICP4 were constructed. These mutant viruses allowed a comparison of gene expression as a function of different domains of ICP4 in the presence and absence of ICP27. Gene expression in the absence of both ICP4 and ICP27 was also examined. The results of this study demonstrate a clear involvement for ICP27 in the induction of early genes, in addition to its known role in enhancing late gene expression during viral infection. In the absence of both ICP4 and ICP27, viral early gene expression, as measured by the accumulation of thymidine kinase and ICP6 messages was dramatically reduced relative to the amounts of these messages seen in the absence of only ICP4. Therefore, elevated levels of early gene expression as a consequence of ICP27 occurred in the absence of any ICP4 activity. Evidence is also presented regarding the modulation of the ICP4 repression function by ICP27. When synthesized in the absence of ICP27, a mutant ICP4 protein was impaired in its ability to repress transcription from the L/ST promoter in the context of viral infection and in vitro. This defect correlated with the loss of the ability of this mutant protein to bind to its recognition sequence when produced in infected cells in the absence of ICP27. These observations indicate that ICP27 can regulate the activity of at least one domain of the ICP4 protein as well as contribute to elevated early gene expression independently of ICP4.

Animals↗

RNA polymerase II holoenzyme modifications accompany transcription reprogramming in herpes simplex virus type 1-infected cells.

During lytic infection, herpes simplex virus type 1 (HSV-1) represses host transcription, recruits RNA polymerase II (RNAP II) to viral replication compartments, and alters the phosphorylation state of the RNAP II large subunit. Host transcription repression and RNAP II modifications require expression of viral immediate-early (IE) genes. Efficient modification of the RNAP II large subunit to the intermediately phosphorylated (IIi) form requires expression of ICP22 and the UL13 kinase. We have further investigated the mechanisms by which HSV-1 effects global changes in RNAP II transcription by analyzing the RNAP II holoenzyme. We find that the RNAP II general transcription factors (GTFs) remain abundant after infection and are recruited into viral replication compartments, suggesting that they continue to be involved in viral gene transcription. However, virus infection modifies the composition of the RNAP II holoenzyme, in particular triggering the loss of the essential GTF, TFIIE. Loss of TFIIE from the RNAP II holoenzyme requires viral IE gene expression, and viral IE proteins may be redundant in mediating this effect. Although viral IE proteins do not associate with the RNAP II holoenzyme, they interact with RNAP II in complexes of lower molecular mass. As the RNAP II holoenzyme containing TFIIE is necessary for activated transcription initiation and RNAP II large subunit phosphorylation in uninfected cells, virus-induced modifications to the holoenzyme may affect both of these processes, leading to aberrant phosphorylation of the RNAP II large subunit and repression of host gene transcription.

HeLa Cells↗

[Experimental study of protective effects of Xuebijing injection on stress-induced organ damage in rabbit].

OBJECTIVE: To investigate the protective effects of the integrated traditional Chinese and western medicine Xuebijing injection on stress-induced organ damage in rabbits. METHODS: Forty rabbits were randomly divided into four groups: the control group, the model group, the western medicine group, and the Xuebijing group. The stress-induced organ damage model was replicated by soak the rabbits in water, the animals in the western medicine group and Xuebijing group received injection of lytic cocktail and Xuebijing, respectively. The changes in cortisol (Cor), thromboxane A(2) (TXA(2)), endothelin (ET), nitric oxide synthase (NOS) were determined at different time points in all the groups. The pathologic changes of the gastric mucosa, the adrenal gland and the cardiac muscle cell were observed. RESULTS: The content of Cor increased significantly in model group (P<0.01). The content of Cor decreased in the western medicine group and Xuebijing group, the changes showed no significant difference between two groups (P>0.05). The contents of ET, TXA(2) decreased and NOS increased in Xuebijing group compared with the western medicine group, the differences were significant (all P<0.05). The pathological changes of the gastric mucosa, the adrenal gland and the cardiac myocyte were less marked in Xuebijing group, compared with the western medicine group, the difference was significant (P<0.05). CONCLUSION: Xuebijing has better protective effects on stress-induced organ damage.

Adrenal Glands↗

Macrophage activity, IL-6 levels, antibody response and heart histology in rats undergoing an attenuated Trypanosoma cruzi acute infection upon treatment with recombinant interferon gamma.

Earlier experiments in Trypanosoma cruzi-infected rats showed that recombinant rat (Rr) interferon (IFN)-gamma given shortly after infection ameliorated acute disease without modifying the serum titers of endogenously synthesized IFN-gamma and tumor necrosis factor. To gain some insight into the processes underlying this protective effect, 21-day old 'I' rats that were infected with T. cruzi and the following day started with a 20-day cycle of RrIFN-gamma injections (20000 IU/rat/day) were investigated for the in vitro replication of T. cruzi and nitric oxide (NO) production by peritoneal macrophages (day 7 post-infection, pi), antibodies with lytic activity against T. cruzi (days 7, 20, and 28 pi), and serum levels of biologically active interleukin (IL)-6 (days 15 and 30 pi). Therapy with RrIFN-gamma rendered cultured peritoneal macrophages less permissive to infection with T. cruzi. Such an effect was not accompanied by higher amounts of NO in macrophage cultured supernatants, compared with those from T. cruzi-infected rats receiving no RrIFN-gamma, which appeared not to be protected from in vitro infection. Acutely T. cruzi-infected rats had significant amounts of IL-6 in their sera - this not being the case in infected rats given RrIFN-gamma, whose levels appeared decreased as in control rats. The presence of complement-mediated anti-T. cruzi lytic antibodies was not modified by RrIFN-gamma. Likewise, heart histology at day 7 pi revealed that treatment with RrIFN-gamma made no differences as to the amount of acute inflammation, but tended to reduce the myocardial parasite load.

Acute Disease↗

A subset of herpes simplex virus replication genes induces DNA amplification within the host cell genome.

Herpes simplex virus (HSV) induces DNA amplification of target genes within the host cell chromosome. To characterize the HSV genes that mediate the amplification effect, combinations of cloned DNA fragments covering the entire HSV genome were transiently transfected into simian virus 40 (SV40)-transformed hamster cells. This led to amplification of the integrated SV40 DNA sequences to a degree comparable to that observed after transfection of intact virion DNA. Transfection of combinations of subclones and of human cytomegalovirus immediate-early promoter-driven expression constructs for individual open reading frames led to the identification of six HSV genes which together were necessary and sufficient for the induction of DNA amplification: UL30 (DNA polymerase), UL29 (major DNA-binding protein), UL5, UL8, UL42, and UL52. All of these genes encode proteins necessary for HSV DNA replication. However, an additional gene coding for an HSV origin-binding protein (UL9) was required for origin-dependent HSV DNA replication but was dispensible for SV40 DNA amplification. Our results show that a subset of HSV replication genes is sufficient for the induction of DNA amplification. This opens the possibility that HSV expresses functions sufficient for DNA amplification but separate from those responsible for lytic viral growth. HSV infection may thereby induce DNA amplification within the host cell genome without killing the host by lytic viral growth. This may lead to persistence of a cell with a new genetic phenotype, which would have implications for the pathogenicity of the virus in vivo.

DNA, Viral↗

Complementation of a herpes simplex virus type 1 Vmw110 deletion mutant by human cytomegalovirus.

The herpes simplex virus type 1 (HSV-1) mutant dl1403 contains a 2 kb deletion within the sequences encoding the immediate early polypeptide Vmw110. Previous experiments showed that although dl1403 exhibits normal patterns of gene expression following infection at an m.o.i. of 5 p.f.u./cell its growth and plaquing efficiency are impaired in low multiplicity infections, particularly in human foetal lung (HFL) cells. We have now investigated the ability of two other human herpesviruses, varicella-zoster virus (VZV) and human cytomegalovirus (HCMV), to compensate for this defect at low m.o.i. in HFL cells. Co-infection with HCMV resulted in greatly increased plaque numbers and the apparent particle/p.f.u. ratios of dl1403 stocks were reduced to values similar to those exhibited by wild-type HSV-1 stocks. Complementation of dl1403 in low multiplicity infections by HCMV and VZV was also demonstrated by an increased yield of the mutant virus and an increase in synthesis of dl1403 DNA. Ultraviolet irradiation of HCMV abolished its ability to complement dl1403 and the presence of adenovirus 5 had no stimulatory effect on dl1403 DNA replication. When HFL monolayers were infected with dilutions of dl1403 stocks such that no plaques were produced, replication of the mutant virus could be induced by superinfection with HCMV 7 days after the initial infection. These results indicate that a non-lytic interaction between dl1403 and HFL cells is a more likely consequence of a low multiplicity infection than plaque formation.

Adenoviruses, Human↗

Interactions of polyoma and mouse DNAs. I. Lytic infection of bromodeoxyuridine-prelabeled mouse embryo cells.

On CsCl isopycnic centrifugation of the DNA extracted from secondary mouse embryo (ME) cultures grown in the presence of 5-bromodeoxyuridine (BUdR) and 5-fluorodeoxyuridine (FUdR) for 40 h, 10 to 25% of the DNA was found to be unsubstituted, 70 to 80% was bromouracil-hybrid DNA, and 5 to 10% was heavy DNA. These results together with cell number determinations, autoradiography, and Feulgen microspectrophotometry revealed three types of cells in these cultures: (i) 60 to 80% of the cells replicated their DNA once, divided, and then stopped mitotic activity, (ii) 5 to 10% were going through a second round of DNA replication; whereas (iii) 10 to 30% did not replicate DNA during the BUdR-FUdR exposure. After the transfer of these cultures to normal medium (without BUdR-FUdR), up to 20% of the cells resumed DNA synthesis asynchronously within 60 h, but no increase in cell number was observed. BUdR-FUdR-treated cultures, which were infected with polyoma virus in the absence of the thymidine analogues, supported a lytic infection to the same extent as did untreated ME cultures. This was concluded from the similar number of cells, which were induced to synthesize DNA, from the similar replication rate of the viral DNA, from the similar number of cells containing polyoma capsid proteins, and from the similar yields of progeny virus determined by hemagglutination and plaque formation. Thus, BUdR-prelabeled ME cultures are suitable for the investigation of interactions of the polyoma and mouse genomes during the lytic infection.

Animals↗

Immunopathology of chronic viral hepatitis.

This paper reviews the main necro-inflammatory liver lesions observed in chronic viral hepatitis B and their apparent immunological mechanisms. Focal necrosis seems to represent the mechanism for clearance of virus replicating hepatocytes by cytotoxic T lymphocytes under HLA class I restriction and with hepatitis B virus nucleocapsid antigens as target antigen. Piecemeal necrosis involves CD8+ lymphocytes, possibly with hepatocellular membrane autoantigens as target antigen. Confluent lytic necrosis (bridging hepatic necrosis) presumably results from humoral immune mechanisms. Focal necrosis, piecemeal necrosis and confluent lytic necrosis determine the extent of necro-inflammatory activity in liver biopsy specimens, classified as chronic persistent hepatitis (low activity) or chronic active hepatitis (high activity). The extent of necro-inflammatory activity fluctuates during the natural course of chronic viral hepatitis B: from low activity during the viral replicative phase, through high activity in the viral elimination phase, into low activity again in the ensuing viral integration phase. The role of HLA antigens, intercellular adhesion molecules, cytokines and accessory antigen presenting cells is emphasized.

HLA Antigens↗