Immunodeficiency virus rev trans-activator modulates the expression of the viral regulatory genes

The pathogenic human retrovirus human immunodeficiency virus type 1 (HIV-1) encodes two trans-acting nuclear proteins, tat and rev, whose functional expression is essential for viral replication in vitro. The tat protein greatly enhances the expression of both structural and regulatory genes of HIV-1 (linked to the viral long-terminal-repeat promoter element), whereas the rev gene product (previously termed art or trs) has only been shown to be required for the synthesis of structural proteins. Here, we demonstrate that rev also moderates the expression of regulatory genes of HIV-1. It decreases the expression of messenger RNAs that encode the full-length form of the viral tat gene product or the rev protein itself, and induces the synthesis of a previously unreported, truncated tat protein. These actions of rev are mediated by a dramatic shift in the ratio of spliced to unspliced cytoplasmic HIV-1 mRNA. Therefore rev not only activates the synthesis of the viral structural proteins, but also modulates the level and quality of HIV-1 regulatory gene expression.     

Expression of the HTLV-III envelope gene by a recombinant vaccinia virus

The discovery that the aetiological agent of acquired immune deficiency syndrome (AIDS) is a retrovirus, referred to as human T-lymphotropic virus type III (HTLV-III) or lymphadenopathy-associated virus (LAV) (for review see ref. 1), has raised the possibility of developing a vaccine. In this regard, the envelope (env) proteins of murine retroviruses can induce protective immunity in mice. The HTLV-III env gene specifies a primary polypeptide of approximately 860 amino acids that is glycosylated to form a precursor of relative molecular mass (Mr) 160,000 (gp160), which gives rise to mature membrane-associated proteins of Mr 120,000 (gp120) and 41,000 (gp41). The HTLV-III env gene has been expressed in Escherichia coli and by simian virus 40 (SV40) vectors but formation of the authentic proteins has not been demonstrated. Here, we describe the expression of the complete env gene by a vaccinia virus vector. Evidence is presented that synthesis, glycosylation, processing and membrane transport of the env polypeptide occurred without other HTLV-III gene functions; the env protein was recognized by sera from unrelated AIDs patients; and a single vaccination with the infectious recombinant vaccinia virus induced antibodies to gp120 in mice.     

Expression of matrix metalloproteinase 9 in nasopharyngeal carcinoma and association with Epstein-Barr virus infection

OBJECTIVE: To evaluate the expression of matrix metalloproteinase-9 (MMP9) in nasopharyngeal carcinoma and the association between MMP9 and Epstein-Barr virus infection. METHODS: The MMP9 expression was studied by immunohistochemical analysis; and Epstein-Barr virus encoded small nuclear mRNA-1 (EBER-1) produced by in situ hybridization were examined in 41 nasopharyngeal carcinoma sections, and the relation between them, and the associations of MMP9 with clinical features were statistically analyzed. RESULTS: Positive expression rate of MMP9 was 73.17%. The expression of MMP9 showed significant positive correlation with the expression of EBER-1 (gamma=0.483, P=0.001). There was significant association of MMP9 expression with lymph nodes metastasis and clinical stage (P<0.001), non-significant association with age, gender, pathological classification and T classification. CONCLUSIONS: The highly pronounced expression of MMP9 is associated with cervical lymph nodes metastasis. Epstein-Barr virus can enhance NPC metastasis by up-regulating the expression of MMP9.     

Transient FTY720 treatment promotes immune-mediated clearance of a chronic viral infection

For a wide variety of microbial pathogens, the outcome of the infection is indeterminate. In some individuals the microbe is cleared, but in others it establishes a chronic infection, and the factors that tip this balance are often unknown. In a widely used model of chronic viral infection, C57BL/6 mice clear the Armstrong strain of lymphocytic choriomeningitis virus (LCMV), but the clone 13 strain persists. Here we show that the Armstrong strain induces a profound lymphopenia at days 1-3 after infection, but the clone 13 strain does not. If we transiently augment lymphopenia by treating the clone-13-infected mice with the drug FTY720 at days 0-2 after infection, the mice successfully clear the infection by day 30. Clearance does not occur when CD4 T cells are absent at the time of treatment, indicating that the drug is not exerting direct antiviral effects. Notably, FTY720 treatment of an already established persistent infection also leads to viral clearance. In both models, FTY720 treatment preserves or augments LCMV-specific CD4 and CD8 T-cell responses, a result that is counter-intuitive because FTY720 is generally regarded as a new immunosuppressive agent. Because FTY720 targets host pathways that are completely evolutionarily conserved, our results may be translatable into new immunotherapies for the treatment of chronic microbial infections in humans.     

Isolation of a human gene that inhibits HIV-1 infection and is suppressed by the viral Vif protein

Viruses have developed diverse non-immune strategies to counteract host-mediated mechanisms that confer resistance to infection. The Vif (virion infectivity factor) proteins are encoded by primate immunodeficiency viruses, most notably human immunodeficiency virus-1 (HIV-1). These proteins are potent regulators of virus infection and replication and are consequently essential for pathogenic infections in vivo. HIV-1 Vif seems to be required during the late stages of virus production for the suppression of an innate antiviral phenotype that resides in human T lymphocytes. Thus, in the absence of Vif, expression of this phenotype renders progeny virions non-infectious. Here, we describe a unique cellular gene, CEM15, whose transient or stable expression in cells that do not normally express CEM15 recreates this phenotype, but whose antiviral action is overcome by the presence of Vif. Because the Vif:CEM15 regulatory circuit is critical for HIV-1 replication, perturbing the circuit may be a promising target for future HIV/AIDS therapies.     

Maintenance of an unfolded polypeptide by a cognate chaperone in bacterial type III secretion.

Many bacterial pathogens use a type III protein secretion system to deliver virulence effector proteins directly into the host cell cytosol, where they modulate cellular processes. A requirement for the effective translocation of several such effector proteins is the binding of specific cytosolic chaperones, which typically interact with discrete domains in the virulence factors. We report here the crystal structure at 1.9 A resolution of the chaperone-binding domain of the Salmonella effector protein SptP with its cognate chaperone SicP. The structure reveals that this domain is maintained in an extended, unfolded conformation that is wound around three successive chaperone molecules. Short segments from two different SptP molecules are juxtaposed by the chaperones, where they dimerize across a hydrophobic interface. These results imply that the chaperones associated with the type III secretion system maintain their substrates in a secretion-competent state that is capable of engaging the secretion machinery to travel through the type III apparatus in an unfolded or partially folded manner.     

Development of a preventive vaccine for Ebola virus infection in primates

Outbreaks of haemorrhagic fever caused by the Ebola virus are associated with high mortality rates that are a distinguishing feature of this human pathogen. The highest lethality is associated with the Zaire subtype, one of four strains identified to date. Its rapid progression allows little opportunity to develop natural immunity, and there is currently no effective anti-viral therapy. Therefore, vaccination offers a promising intervention to prevent infection and limit spread. Here we describe a highly effective vaccine strategy for Ebola virus infection in non-human primates. A combination of DNA immunization and boosting with adenoviral vectors that encode viral proteins generated cellular and humoral immunity in cynomolgus macaques. Challenge with a lethal dose of the highly pathogenic, wild-type, 1976 Mayinga strain of Ebola Zaire virus resulted in uniform infection in controls, who progressed to a moribund state and death in less than one week. In contrast, all vaccinated animals were asymptomatic for more than six months, with no detectable virus after the initial challenge. These findings demonstrate that it is possible to develop a preventive vaccine against Ebola virus infection in primates.     

The pathogenicity on legumes of Cucumber mosaic virus was determined by 243 nucleotides on 2a polymerase gene of viral RNA2

We had isolated and identified two Cucumber mosaic virus (CMV) isolates, the CMV red bean (CMV-RB)isolate and the CMV pea (CMV-P1) isolate. CMV-RBinduces necrotic local lesions on inoculated leaves of broad bean, pea, cowpea and bean, and could not infect these hosts systemically. However, CMV-P1 was able to infect these legumes systemically. To study the difference of pathogenicity. on the legumes induced by these two CMV isolates, the full-length infectious cDNA clones of CMV-Fny, which induced similar symptoms as CMV-RB in the four legumes,were used. The 243 nucleotides fragment, which encodes highly conserved GDD amino acid motif on 2a replicase gene of CMV-Fny RNA2, was replaced with that of CMV-P1. The constructed chimeric virus FP could infect these legumes systemically. The exchange of this region changes the virus symptoms on the legumes, indicating that this 243 nucleotides fragment has major effect on pathogenicity of CMV on the legumes.``     

Membrane leakiness after viral infection and a new approach to the development of antiviral agents.

Viral development induces changes in the permeability properties of the plasma membrane of the host cell. Here it is shown that, because of this leakiness, inhibitors of protein synthesis normally impermeable to uninfected cells are able to enter infected cells and thereby specifically inhibit viral protein synthesis.     

Prevention of vaccinia virus infection in immunodeficient mice by vector-directed IL-2 expression

Recombinant vaccinia viruses have been proposed as live vaccines against a variety of infectious diseases, including AIDS (acquired immune deficiency syndrome). Objections have been concerned primarily with side effects of the vaccinia virus vector itself. Recently it has been shown that inactivation of the vaccinia virus thymidine kinase gene or deletion of certain other non-essential genes is associated with a marked reduction in pathogenicity. Nevertheless, the ability of vaccinia virus to produce a progressive infection in immunodeficient individuals remains a most serious problem. Indeed, an incident of this type in a vaccinated man seropositive for human immunodeficiency virus was recently reported. We have used immunodeficient athymic nude mice to establish a model of disseminated vaccinia virus infection, and to demonstrate a novel approach to virus attenuation which involves insertion of a gene encoding human interleukin-2 into the genome of vaccinia virus vectors.     

新型截断圆形波导的阶梯近似直线法分析

用直线法分析了一种新型截断圆形波导,对其传输特性进行了数值计算和分析,并验证了分析方法的正确性.该方法具有推导简便、计算量小等优点,可作为研究新型截断圆形波导及处理电磁场边值问题的参考.     

蝇蛆提高对虾抗杆状病毒感染能力的初步研究1

室内试验表明,投饲蝇蛆起始时间至少需在病毒侵袭前10 d,对对虾起始死亡时间和50%,90%死亡时间才有明显的延缓,分别较对照组延长1.76,3.04,4.1倍;蝇蛆可以显著提高对虾的抗杆状病毒感染能力,激活对虾的酚氧化酶系统.田间试验表明,投喂有蝇蛆的虾池,存活时间平均为64 d,不投喂蝇蛆的对虾,存活时间平均为33.5 d.1993年投喂蝇蛆的虾池平均每天死虾数小于存池量的0.023%,1994年平均每天死虾数占存池数的0.015% ,经PCR检测证实,1993,1994 年对虾中杆状病毒病变的个体仅占1.15%.     

Evolvability of an RNA virus is determined by its mutational neighbourhood

The ubiquity of mechanisms that generate genetic variation has spurred arguments that evolvability, the ability to generate adaptive variation, has itself evolved in response to natural selection. The high mutation rate of RNA viruses is postulated to be an adaptation for evolvability, but the paradox is that whereas some RNA viruses evolve at high rates, others are highly stable. Here we show that evolvability in the RNA bacteriophage phi6 is also determined by the accessibility of advantageous genotypes within the mutational neighbourhood (the set of mutants one or a few mutational steps away). We found that two phi6 populations that were derived from a single ancestral phage repeatedly evolved at different rates and toward different fitness maxima. Fitness measurements of individual phages showed that the fitness distribution of mutants differed between the two populations. Whereas population A, which evolved toward a higher maximum, had a distribution that contained many advantageous mutants, population B, which evolved toward a lower maximum, had a distribution that contained only deleterious mutants. We interpret these distributions to measure the fitness effects of genotypes that are mutationally available to the two populations. Thus, the evolvability of phi6 is constrained by the distribution of its mutational neighbours, despite the fact that this phage has the characteristic high mutation rate of RNA viruses.     

Duplications of a mutated simian virus 40 enhancer restore its activity

Enhancers are cis-acting control elements which can stimulate at a distance the activity of a variety of eukaryotic promoters. First identified as a repeated 72 base pair (bp) sequence upstream of the simian virus 40 (SV40) early gene promoter, enhancers have since been shown to be associated with numerous other viral and cellular genes. Although there are no strong homologies between the sequences of different enhancers, a number of short and degenerate consensus sequences have been identified, including the 'core' element GTGGA/TA/TA/TG and stretches of alternating purines and pyrimidines which may have the potential to form left-handed Z DNA. To study the functional significance of two alternating purine and pyrimidine sequences in the SV40 enhancer, we have introduced various combinations of point mutations into a modified SV40 enhancer which contained only one copy of the 72 bp element (W.H., Y.G., A. Nordheim and A. Rich, unpublished results); one of these combinations impaired both the activity of the enhancer and growth of SV40. We describe here the structure of 18 revertants of this mutant and suggest that in each of the 18 revertants, the defects of the original mutant have been overcome by simple tandem duplications in the enhancer region, all of which include the 'core' element.