Evolutionary relationship of alfalfa mosaic virus with cucumber mosaic virus and brome mosaic virus

The amino acid sequences of the non-structural protein (molecular weight 35,000; 3a protein) from three plant viruses — cucumber mosaic, brome mosaic and alfalfa mosaic have been systematically compared using the partial genomic sequences for these three viruses already available. The 3a protein of cucumber mosaic virus has an amino acid sequence homology of 33.7% with the corresponding protein of brome mosaic virus. A similar protein from alfalfa mosaic virus has a homology of 18.2% and 14.2% with the protein from brome mosaic virus and cucumber mosaic virus, respectively. These results suggest that the three plant viruses are evolutionarily related, although, the evolutionary distance between alfalfa mosaic virus and cucumber mosaic virus or brome mosaic virus is much larger than the corresponding distance between the latter two viruses.     

Reassembly of brome mosaic virus from dissociated virus

The reconstitution of Brome Mosaic Virus (BMV) has been studied using neutron scattering. Experiments were performed on disassembled virus without subsequent separation of components. Phase diagrams of the disassembly and subsequent reassembly of BMV were established as a function of pH and LiCl molarity by analytical centrifugation and quasi-elastic light scattering. Disassembly occurs at a pH above 6.5 and above 0.8 M LiCl. On reassembly, if the pH is lowered first, capsids are formed without subsequent incorporation of RNA. Neutron scattering was used to investigate the formation of virus particles, when the ionic strength was lowered from 1.4 to 0.1 M LiCl at pH 7.8. The reconstitution was followed continuously. As it was driven by a lowering of the ionic strength the kinetics of the process cannot be studied for short times. However the fact that at any given ionic strength no evolution of the scattering was observed with time implies that the reconstitution is complete within a few minutes. The observations in buffers with various amounts of D₂O lead to the conclusion that the reassembly is achieved by co-condensation of the RNA and of the capsid proteins.     

The biology of Chilo iridescent virus

Chilo iridescent virus (CIV) is the type species for genus Iridovirus, and belongs to the family Iridoviridae. Since the discovery of CIV in 1966, many attempts were made to elucidate the viral genome structure. The virions contain a single linear ds DNA molecule that is circularly permuted and terminally redundant. The genome of CIV has been entirely sequenced. The CIV virion consists of an unusual three-layer structure containing an outer proteinaceous capsid, an intermediate lipid membrane, and a core DNA-protein complex containing the genome. CIV has a broad host spectrum and has, in general, a limited mortality effect on its hosts. Up to now there have been several studies about CIV describing its structure, ecology, and molecular biology. In this review study we present all these studies together to describe the CIV.     

Herpes simplex virus co-infection facilitates rolling circle replication of the adeno-associated virus genome

Adeno-associated virus (AAV) genome replication only occurs in the presence of a co-infecting helper virus such as adenovirus type 5 (AdV5) or herpes simplex virus type 1 (HSV-1). AdV5-supported replication of the AAV genome has been described to occur in a strand-displacement rolling hairpin replication (RHR) mechanism initiated at the AAV 3’ inverted terminal repeat (ITR) end. It has been assumed that the same mechanism applies to HSV-1-supported AAV genome replication. Using Southern analysis and nanopore sequencing as a novel, high-throughput approach to study viral genome replication we demonstrate the formation of double-stranded head-to-tail concatemers of AAV genomes in the presence of HSV-1, thus providing evidence for an unequivocal rolling circle replication (RCR) mechanism. This stands in contrast to the textbook model of AAV genome replication when HSV-1 is the helper virus.     

The structure of cucumber mosaic virus and comparison to cowpea chlorotic mottle virus

The structure of cucumber mosaic virus (CMV; strain Fny) has been determined to a 3.2-A resolution using X-ray crystallography. Despite the fact that CMV has only 19% capsid protein sequence identity (34% similarity) to cowpea chlorotic mottle virus (CCMV), the core structures of these two members of the Bromoviridae family are highly homologous. As suggested by a previous low-resolution structural study, the 305-A diameter (maximum) of CMV is approximately 12 A larger than that of CCMV. In CCMV, the structures of the A, B, and C subunits are nearly identical except in their N termini. In contrast, the structures of two loops in subunit A of CMV differ from those in B and C. These loops are 6 and 7 residues longer than the analogous regions in CCMV. Unlike that of CCMV, the capsid of CMV does not undergo swelling at pH 7.0 and is stable at pH 9.0. This may be partly due to the fact that the N termini of the B and C subunits form a unique bundle of six amphipathic helices oriented down into the virion core at the threefold axes. In addition, while CCMV has a cluster of aspartic acid residues at the quasi-threefold axis that are proposed to bind metal in a pH-dependent manner, this cluster is replaced by complementing acids and bases in CMV. Finally, this structure clearly demonstrates that the residues important for aphid transmission lie at the outermost portion of the betaH-betaI loop and yields details of the portions of the virus that are hypothesized to mediate binding to aphid mouthparts.     

The ecology of Ebola virus

Since Ebola virus was first identified more than 30 years ago, tremendous progress has been made in understanding the molecular biology and pathogenesis of this virus. However, the means by which Ebola virus is maintained and transmitted in nature remains unclear despite dedicated efforts to answer these questions. Recent work has provided new evidence that fruit bats might have a role as a reservoir species, but it is not clear whether other species are also involved or how transmission to humans or apes takes place. Two opposing hypotheses for Ebola emergence have surfaced; one of long-term local persistence in a cryptic and infrequently contacted reservoir, versus another of a more recent introduction of the virus and directional spread through susceptible populations. Nevertheless, with the increasing frequency of human filovirus outbreaks and the tremendous impact of infection on the already threatened great ape populations, there is an urgent need to better understand the ecology of Ebola virus in nature.     

Respiratory syncytial virus

Human respiratory syncytial virus (RSV) is the most common worldwide cause of lower respiratory tract infections (LRI) in infants less than 6 months of age. The prophylaxis against RSV infection by vaccination has been unsuccessful because of its adverse effects. As antiviral drug, ribavirin spray (aerosol) had been used clinically and reduces the amount of virus load, without reducing the necessity of symptomatic therapy and the duration of hospitalization. Therefore RSV LRI has been treated mainly symptomatically. Recently humanized anti-RSV F protein monoclonal antibody was developed and prescribed for prevention in high-risk infants such as premature ones and those with chronic lung and congenital heart diseases. It reduced the incidence of hospitalization significantly. It has been introduced in clinical use in Japan following to Western countries. On the other hand, a number of anti-RSV drugs have now been investigation; however, no valuable drugs for clinical use have been yet developed.     

The hepatitis B virus and its DNA polymerase: The prototype three-D virus

Summary The hepatitis B virus (HBV), the causal agent of serum hepatitis, has a diameter of 42 nm and is comprised of an outer surface coat and a 27 nm core. A unique DNA-dependent DNA polymerase is associated with the core of the virus. The core also houses a circular DNA that contains both double-stranded and single-stranded regions. In the endogenous reaction, the DNA polymerase repairs the single-stranded gaps of the viral DNA. The surface protein of the virus, called hepatitis B surface antigen, contains both lipid and carbohydrate, and is often present in particulate form in the blood of infected patients. In Asia and Africa HBV infection is associated with subsequent development of primary hepatocellular carcinoma. Although most patients recover completely from acute illness, the hepatitis B virus may cause chronic infection. Recently, a virus similar to human HBV was discovered in woodchucks. HBV has not yet been propagated in a cell culture system and the mode of replication of this unusual virus in hepatocytes is still moot. Although reliable therapy has not yet been provided, the problem of this world-wide infection has led to many interesting approaches to both vaccine production and anti-viral chemotherapy.     

The immunology of Epstein-Barr virus infection

Epstein-Barr virus is a classic example of a persistent human virus that has caught the imagination of immunologists, virologists and oncologists because of the juxtaposition of a number of important properties. First, the ability of the virus to immortalize B lymphocytes in vitro has provided an antigen presenting cell in which all the latent antigens of the virus are displayed and are available for systematic study. Second, the virus presents an ideal system for studying the immune parameters that maintain latency and the consequences of disturbing this cell-virus relationship. Third, this wealth of immunological background has provided a platform for elucidating the role of the immune system in protection from viral-associated malignancies of B cell and epithelial cell origin. Finally, attention is now being directed towards the development of vaccine formulations which might have broad application in the control of human malignancies.     

Simian homologues of Epstein-Barr virus

Gamma-herpesviruses closely related to the Epstein-Barr virus (EBV) are known to naturally infect Old World non-human primates and are classified in the same lymphocryptovirus (LCV) genera. LCV infecting humans and Old World primates share similar biology, and recent studies have demonstrated that these viruses share a similar repertoire of viral genes. Surprisingly, the latent infection genes associated with cell growth transformation demonstrate the most striking sequence divergence, but the functional mechanisms for these genes are generally well conserved. The recent discovery of LCVs naturally infecting New World primates has rewritten the old paradigm of LCV host range restriction to humans and Old World non-human primates, so that these viruses are more widespread than previously believed. However, the New World LCV genome has significant and interesting differences from EBV and other Old World LCVs despite similar biological properties. Thus, the simian homologues of EBV can provide an important animal model for studying LCV pathogenesis, and the similarities and differences that have evolved among these related viruses can provide a unique perspective towards a better understanding of EBV.     

巨大病毒的发现及研究进展

人们发现第一个病毒以来,病毒学科取得了迅猛的发展,人们对病毒大小的认知也已经基本成型。21世纪初,科学家发现了拟菌病毒,开启了巨大病毒的大门,此后人们又陆续发现了多种巨大病毒。这些病毒体积较大,基因复杂,已经超出了以往以大小区分病毒的标准,其体积和基因组大小甚至与很多原核和真核生物相当。此外,科学家们还发现了数种能够感染巨大病毒和其他核质大DNA病毒(nucleocytoplasmic large DNA virus,NCLDV)的病毒,将其命名为噬病毒体。这一系列新发现极大地触动了人们对病毒认识的知识体系,并导致了关于病毒起源与进化问题的讨论,这在病毒学史上具有重大的意义。     

TT virus

Non-enveloped TT virus (TTV), recognized in 1997, contains single-stranded circular DNA (about 3,800 nucleotides) and seems to be a member of Circinoviridae, a new family of hepatitis viruses. The data on the occurrence of TTV are highly controversial: 1-22% in blood donors, 20-40% in hematological patients, 15-35% in patients with liver diseases. The virus has been found to be transmitted by the oral-fecal route as it penetrates via bile into feces and is then excreted from the gastrointestinal tract. A relatively low percentage of the occurrence of TTV infection in groups of risk may be regarded as the evidence that sexual and injection routes are not the main route of its transmission. Further investigations are necessary to establish the regularities of the epidemiology of TTV, to obtain information on its pathogenicity and on the methods for diagnosing hepatitis caused by this virus.     

Properties of the Ebola virus glycoprotein

In central and west Africa, Ebola virus, a member of the filovirus group, has produced sporadic outbreaks of lethal disease. This virus causes hemorrhagic fever in humans and nonhuman primates, resulting in mortality rates of up to 90%. Although there are no satisfactory biologic explanations for this extreme virulence, it has been suggested that functions of the envelope glycoprotein are likely to play important roles in the pathogenicity of Ebola virus.     

Tobacco mosaic virus and the study of early events in virus infections

In order to establish infections, viruses must be delivered to the cells of potential hosts and must then engage in activities that enable their genomes to be expressed and replicated. With most viruses, the events that precede the onset of production of progeny virus particles are referred to as the early events and, in the case of positive-strand RNA viruses, they include the initial interaction with and entry of host cells and the release (uncoating) of the genome from the virus particles. Though the early events remain one of the more poorly understood areas of plant virology, the virus with which most of the relevant research has been performed is tobacco mosaic virus (TMV). In spite of this effort, there remains much uncertainty about the form or constituent of the virus that actually enters the initially invaded cell in a plant and about the mechanism(s) that trigger the subsequent uncoating (virion disassembly) reactions. A variety of approaches have been used in attempts to determine the fate of TMV particles that are involved in the establishment of an infection and these are briefly described in this review. In some recent work, it has been proposed that the uncoating process involves the bidirectional release of coat protein subunits from the viral RNA and that these activities may be mediated by cotranslational and coreplicational disassembly mechanisms.     

Infection of chicken embryonic fibroblasts by measles virus: adaptation at the virus entry level

Measles virus (MV) has a tropism restricted to humans and primates and uses the human CD46 molecule as a cellular receptor. MV has been adapted to grow in chicken embryonic fibroblasts (CEF) and gave rise to an attenuated live vaccine. Hallé and Schwarz MV strains were compared in their ability to infect both simian Vero cells and CEF. Whereas both strains infected Vero cells, only the CEF-adapted Schwarz strain was able to efficiently infect CEF. Since the expression of the human MV receptor CD46 rendered the chicken embryonic cell line TCF more permissive to the infection by the Hallé MV strain, the MV entry into CEF appeared to be a limiting step in the absence of prior MV adaptation. CEF lacked reactivity with anti-CD46 antibodies but were found to express another protein allowing MV binding as an alternative receptor to CD46.     

我国西尼罗病毒和Tahyna病毒的发现与流行

已发现100余种蚊传虫媒病毒在世界各地流行,其引发的人兽共患病是全世界关注的公共卫生问题。长期以来我国仅发现乙型脑炎和登革热两种蚊传虫媒病毒病,但近年来新发现西尼罗病毒和Tahyna病毒及其感染疾病流行。从我国新疆维吾尔自治区采集的蚊虫标本中分离到西尼罗病毒,大量血清学研究证明当地不仅存在西尼罗病毒感染所致疾病,还发生过西尼罗病毒感染引发的病毒性脑炎流行。目前已从新疆维吾尔自治区、青海省和内蒙古自治区采集的蚊虫标本中分离到Tahyna病毒,并发现其在自然界动物中的循环和导致的人类感染流行。西尼罗病毒和Tahyna病毒及其相关感染性疾病的发现为我国虫媒病毒及虫媒病毒病的预防与控制提出了新的挑战。     

A model for persistent infection with Epstein-Barr virus: the stealth virus of human B cells.

Most adult humans are infected benignly and for life with the herpesvirus Epstein-Barr virus. EBV has been a focus of research because of its status as a candidate tumor virus for a number of lymphomas and carcinomas. In vitro EBV has the ability to establish a latent infection in proliferating B lymphoblasts. This is the only system available for studying human herpesvirus latency in culture and has been extremely useful for elucidating how EBV promotes cellular growth. However, to understand how EBV survives in the healthy host and what goes awry, leading to disease, it is essential to know how EBV establishes and maintains a persistent infection in vivo. Early studies on the mechanism of EBV persistence produced inconclusive and often contradictory results because the techniques available were crude and insensitive. Recent advances in PCR technology and the application of sophisticated cell fractionation techniques have now provided new insights into the behavior of the virus. Most dramatically it has been shown that EBV in vivo does not establish latency in a proliferating lymphoblast, but in a resting memory B cell. The contrasting behaviors of being able to establish a latent infection in proliferating B blasts and resting memory B cells can be resolved in terms of a model where EBV performs its complete life cycle in B lymphocytes. The virus achieves this not by disrupting normal B cell biology but by using it.     

Epidemiologic interference of virus populations

Summary There are a few simulation studies for interference models in the literature but the present paper discusses an analytical model for the competition of two interfering virus populations in a community. The mathematical model consist of eight coupled differential equations which have up to four equilibrium points. Criteria for local stability are given.This paper has been read at the workshop on Nonlinear Models in Biology and Medicine, 23rd Biometric Colloquium, German Region of the Biometric Society, Nuremberg, March 1977