Toxic clumps of the protein have been found in the brains of people who had Alzheimer's when they died. The new study started as a search for new Alzheimer's treatments in the vast repository of drugs that have already been approved for use in other diseases. In order to do this, the teams had to create maps of the various genetic and biological networks of Alzheimer's disease so that they could compare them and how they might be affected by different drugs.
It was during this process that they discovered that Alzheimer's likely involves a complex mix of factors, including genetic features of the person with the disease and the viruses that they are exposed to during their lives. Using data from a range of brain banks and cohort studies, the team took a step-by-step approach.
They identified likely viral sequences with the help of information from the Mount Sinai Brain Bank.
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By adding data from the Emory Alzheimer's Disease Research Center, the researchers gathered more clues on how the various viral sequences might alter protein levels in the brain. After further analysis using advanced computer models, the team made several important findings. Another important finding was the discovery of several "overlaps" between "virus-host interactions and genes associated with Alzheimer's risk. The researchers also found evidence involving genes, transcription of genes, and proteins of several viruses influencing Alzheimer's disease biology.
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Register take the tour. By Catharine Paddock PhD. The multiple components of such viruses assemble within infected cells in stages, first into subviral particles and then into completed virions.
Computer virus - Wikipedia
The genomes of these complex viruses encode proteins that assist in the assembly of the virion , but the assembly proteins are not themselves components of the completed virion. A virus that infects only bacteria is called a bacteriophage , or simply a phage. Viruses that infect animal or plant cells are referred to generally as animal viruses or plant viruses. A few viruses can grow in both plants and the insects that feed on them. The highly mobile insects serve as vectors for transferring such viruses between susceptible plant hosts. An example is potato yellow dwarf virus, which can grow in leafhoppers insects that feed on potato plant leaves as well as in potato plants.
Wide host ranges are characteristic of some strictly animal viruses, such as vesicular stomatitis virus, which grows in insects and in many different types of mammalian cells. Most animal viruses, however, do not cross phyla, and some e. The host-cell range of some animal viruses is further restricted to a limited number of cell types because only these cells have appropriate surface receptors to which the virions can attach.
The number of infectious viral particles in a sample can be quantified by a plaque assay. This assay is performed by culturing a dilute sample of viral particles on a plate covered with host cells and then counting the number of local lesions, called plaques, that develop Figure A plaque develops on the plate wherever a single virion initially infects a single cell.
The virus replicates in this initial host cell and then lyses the cell, releasing many progeny virions that infect the neighboring cells on the plate. After a few such cycles of infection, enough cells are lysed to produce a visible plaque in the layer of remaining uninfected cells. Plaque assay for determining number of infectious particles in a viral suspension. Since all the progeny virions in a plaque are derived from a single parental virus , they constitute a virus clone. This type of plaque assay is in standard use for bacterial and animal viruses.
Plant viruses can be assayed similarly by counting local lesions on plant leaves inoculated with viruses. Analysis of viral mutants, which are commonly isolated by plaque assays, has contributed extensively to current understanding of molecular cellular processes. The surface of viruses includes many copies of one type of protein that binds, or adsorbs, specifically to multiple copies of a receptor protein on a host cell. This interaction determines the host range of a virus and begins the infection process Figure The entering genetic material may still be accompanied by inner viral proteins, although in the case of many bacteriophages, all capsid proteins remain outside an infected cell.
The genome of most DNA-containing viruses that infect eukaryotic cells is transported with some associated proteins into the cell nucleus , where the cellular DNA is, of course, also found. The viral mRNA that is produced then is translated into viral proteins by host-cell ribosomes, tRNA, and translation factors. Electron micrograph of a T4 bacteriophage adsorbed onto an E. Once viral surface proteins interact with receptors on the host cell, the viral DNA is injected into the cell.
Levine, , Viruses, Scientific American Library, p. Most viral protein products fall into one of three categories: These last proteins generally are made in much larger amounts than the other two types. After the synthesis of hundreds to thousands of new virions has been completed, most infected bacterial cells and some infected plant and animal cells rupture, or lyse, releasing all the virions at once.
In many plant and animal viral infections, however, no discrete lytic event occurs; rather, the dead host cell releases the virions as it gradually disintegrates. The outcome is the production of a new round of viral particles and death of the cell. Figure illustrates the lytic cycle for T4 bacteriophage. Adsorption and release of enveloped animal viruses are somewhat more complicated processes. The steps in the lytic replication cycle of a nonenveloped virus are illustrated for E. During adsorption step 1 , viral coat proteins at the tip of the tail in T4 interact with specific more We illustrate the lytic cycle of enveloped viruses with the rabies virus , whose nucleocapsid consists of a single-stranded RNA genome surrounded by multiple copies of nucleocapsid protein Figure , upper left.
Within the nucleocapsid of rabies virions are viral enzymes for synthesizing viral mRNA and replicating the viral genome. The envelope around the nucleocapsid is a phospholipid bilayer containing multiple copies of a viral transmembrane glycoprotein. The internal domain interacts with the viral matrix protein, which functions as a bridge between the transmembrane glycoprotein and nucleocapsid protein. Figure outlines the events involved in adsorption of a rabies virion , assembly of progeny nucleocapsids, and release of progeny virions by budding from the host-cell plasma membrane.
Budding virions are clearly visible in electron micrographs, as illustrated by Figure The steps in the lytic replication cycle of an enveloped virus are illustrated for rabies virus, which has a single-stranded RNA genome. The structural components of this virus are depicted at the top. Note that the nucleocapsid of this virus is helical more Transmission electron micrograph of measles virus budding from the surface of an infected cell. This association is called lysogeny , and the integrated phage DNA is referred to as a prophage Figure Under certain conditions, the prophage DNA is activated, leading to its excision from the host-cell chromosome and entrance into the lytic cycle.
Bacterial viruses of this type are called temperate phages. The genomes of a number of animal viruses also can integrate into the host-cell genome. Probably the most important are the retroviruses, described briefly later in this chapter. The linear double-stranded DNA is converted to a circular form immediately after infection. Left If the nutritional state of the host cell is favorable, more A few phages and animal viruses can infect a cell and cause new virion production without killing the cell or becoming integrated.
Bacterial viruses have played a crucial role in the development of molecular cell biology. Thousands of different bacteriophages have been isolated; many of these are particularly well suited for studies of specific biochemical or genetic events. Here, we briefly describe four types of bacteriophages, all of which infect E. The T phages of E.
After the tip of a T-phage tail adsorbs to receptors on the surface of an E. The phage DNA then directs a program of events that produces approximately new phage particles in about 20 minutes, at which time the infected cell lyses and releases the new phages. The initial discovery of the role of messenger RNA in protein synthesis was based on studies of E.
By 20 minutes after infection, infected cells synthesize T2 proteins only. This phage has one of the most studied genomes and is used extensively in DNA cloning Chapter 7. On entering an E. In the latter case, proteins expressed from the viral DNA bind a specific sequence on the circular viral DNA to a similar specific sequence on the circular bacterial DNA.
Alzheimer's: 'Strong evidence' of virus involvement
These were the first organisms in which the entire DNA sequence of a genome was determined, permitting extensive understanding of the viral life cycle. The viruses in this group are so simple that they do not encode most of the proteins required for replication of their DNA but depend on cellular proteins for this purpose. For this reason, they have been particularly useful in identifying and analyzing the cellular proteins involved in DNA replication Chapter In one of the earliest demonstrations that cell-free protein synthesis can be mediated by mRNA, RNA from these phages was shown to direct the synthesis of viral coat protein when added to an extract of E.
These viruses, among the smallest known, encode only four proteins: Animal viruses come in a variety of shapes, sizes, and genetic strategies. In this book, we are concerned with viruses that exhibit at least one of two features: The names of many viruses are based on the names of the diseases they cause or of the animals or plants they infect.
Common examples include poliovirus, which causes poliomyelitis; tobacco mosaic virus , which causes a mottling disease of tobacco leaves; and human immunodeficiency virus HIV , which causes acquired immunodeficiency syndrome AIDS. However, many different kinds of viruses often produce the same symptoms or the same apparent disease states; for example, several dozen different viruses can cause the red eyes, runny nose, and sneezing referred to as the common cold.
Clearly, any attempt to classify viruses on the basis of the symptoms they produce or their hosts obscures many important differences in their structures and life cycles. These are normally insects, but some fungi, nematode worms , and single-celled organisms have been shown to be vectors. When control of plant virus infections is considered economical, for perennial fruits, for example, efforts are concentrated on killing the vectors and removing alternate hosts such as weeds.
Plants have elaborate and effective defence mechanisms against viruses. One of the most effective is the presence of so-called resistance R genes. Each R gene confers resistance to a particular virus by triggering localised areas of cell death around the infected cell, which can often be seen with the unaided eye as large spots.
This stops the infection from spreading. Plant virus particles or virus-like particles VLPs have applications in both biotechnology and nanotechnology. The capsids of most plant viruses are simple and robust structures and can be produced in large quantities either by the infection of plants or by expression in a variety of heterologous systems. Plant virus particles can be modified genetically and chemically to encapsulate foreign material and can be incorporated into supramolecular structures for use in biotechnology.
Within a short amount of time, in some cases just minutes, bacterial polymerase starts translating viral mRNA into protein. These proteins go on to become either new virions within the cell, helper proteins, which help assembly of new virions, or proteins involved in cell lysis.
Viral enzymes aid in the breakdown of the cell membrane, and, in the case of the T4 phage , in just over twenty minutes after injection over three hundred phages could be released. The major way bacteria defend themselves from bacteriophages is by producing enzymes that destroy foreign DNA. These enzymes, called restriction endonucleases , cut up the viral DNA that bacteriophages inject into bacterial cells.
Some viruses replicate within archaea: These enable archaea to retain sections of viral DNA, which are then used to target and eliminate subsequent infections by the virus using a process similar to RNA interference. The organic molecules released from the dead bacterial cells stimulate fresh bacterial and algal growth, in a process known as the viral shunt. In January , scientists reported that million viruses, mainly of marine origin, are deposited daily from the Earth 's atmosphere onto every square meter of the planet's surface, as the result of a global atmospheric stream of viruses, circulating above the weather system, but below the altitude of usual airline travel, distributing viruses around the planet.
Like any organism, marine mammals are susceptible to viral infections. In and , thousands of harbour seals were killed in Europe by phocine distemper virus. Viruses are an important natural means of transferring genes between different species, which increases genetic diversity and drives evolution. Viruses are important to the study of molecular and cell biology as they provide simple systems that can be used to manipulate and investigate the functions of cells.
Geneticists often use viruses as vectors to introduce genes into cells that they are studying. This is useful for making the cell produce a foreign substance, or to study the effect of introducing a new gene into the genome. In similar fashion, virotherapy uses viruses as vectors to treat various diseases, as they can specifically target cells and DNA. It shows promising use in the treatment of cancer and in gene therapy.
Eastern European scientists have used phage therapy as an alternative to antibiotics for some time, and interest in this approach is increasing, because of the high level of antibiotic resistance now found in some pathogenic bacteria. Industrial processes have been recently developed using viral vectors and a number of pharmaceutical proteins are currently in pre-clinical and clinical trials. Virotherapy involves the use of genetically modified viruses to treat diseases. Talimogene laherparepvec T-VEC , for example, is a modified herpes simplex virus that has had a gene, which is required for viruses to replicate in healthy cells, deleted and replaced with a human gene GM-CSF that stimulates immunity.
When this virus infects cancer cells, it destroys them and in doing so the presence the GM-CSF gene attracts dendritic cells from the surrounding tissues of the body. The dendritic cells process the dead cancer cells and present components of them to other cells of the immune system. Current trends in nanotechnology promise to make much more versatile use of viruses. From the viewpoint of a materials scientist, viruses can be regarded as organic nanoparticles.
Their surface carries specific tools designed to cross the barriers of their host cells. The size and shape of viruses, and the number and nature of the functional groups on their surface, is precisely defined. As such, viruses are commonly used in materials science as scaffolds for covalently linked surface modifications. A particular quality of viruses is that they can be tailored by directed evolution. The powerful techniques developed by life sciences are becoming the basis of engineering approaches towards nanomaterials, opening a wide range of applications far beyond biology and medicine.
Because of their size, shape, and well-defined chemical structures, viruses have been used as templates for organising materials on the nanoscale. In this application, the virus particles separate the fluorescent dyes used for signalling to prevent the formation of non-fluorescent dimers that act as quenchers. Many viruses can be synthesised de novo "from scratch" and the first synthetic virus was created in That is, they contain all the necessary information to produce new viruses. This technology is now being used to investigate novel vaccine strategies.
As of November [update] , the full-length genome sequences of different viruses, including smallpox, are publicly available in an online database maintained by the National Institutes of Health. The ability of viruses to cause devastating epidemics in human societies has led to the concern that viruses could be weaponised for biological warfare. Further concern was raised by the successful recreation of the infamous influenza virus in a laboratory. Smallpox virus devastated numerous societies throughout history before its eradication.
There are only two centres in the world that are authorised by the WHO to keep stocks of smallpox virus: Thus, much of the modern human population has almost no established resistance to smallpox, and would be vulnerable to the virus. From Wikipedia, the free encyclopedia. This article is about the type of pathogen. For the type of malware, see Computer virus.
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Structure of an icosahedral cowpea mosaic virus.
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