Sequence analysis of viral genomes

The determination of a DNA virus genome sequence provides the ultimate physical description. While there are methods for sequencing RNA molecules, these methods are not applicable to Fig. 11.6 The famous Kleinschmidt electron micrograph of phage T4 DNA extruded from the capsid. Before this photograph was made, there was controversy about whether the viral genome was a single piece of DNA or multiple pieces the fragility of large DNA molecules made them difficult to isolate without shearing....

Viral capsids

The capsid is a complex structure made up of many identical subunits of viral protein often termed a capsomer. The capsid functions to provide a protein shell in which the chemically labile viral genome can be maintained in a stable environment. The association of capsids with genomes is a complex process, but it must result in an energetically stable structure. While viruses can assume a range of shapes, some quite complex, given the dimensions of virus structure and the constraints of the...

Generation of the virion envelope and egress of the enveloped virion

The lipid bilayer of the membrane envelope of the viruses that bear them is derived from the infected cell. Few (if any) viral genes directed toward lipid biosynthesis or membrane assembly are yet identified. While the lipid bilayer is entirely cellular, the envelope is made virus specific by the insertion of one or several virus-encoded membrane proteins that are synthesized during the replication cycle. Some of the patterns of envelopment at the plasma membrane for viruses that assemble in...

Quantitative measure of infectious centers Plaque assays

Cytopathic effects on the host cell by the great majority of viruses cause observable damage or changes to the cells in which they are replicating. Even if cells are not killed or lysed, the alteration of cells in a local area due to a localized virus infection can readily be observed as a plaque or focus of infection. With proper dilutions and conditions, such a localized infection can be the result of infection with a single biologically active virus. A virus particle able to initiate a...

Strategies to Protect Against and Combat Viral Infection

VACCINATION - INDUCTION OF IMMUNITY TO PREVENT VIRUS INFECTION Smallpox and the history of vaccination How a vaccine is produced Live-virus vaccines Killed-virus vaccines Recombinant virus vaccines Capsid and subunit vaccines DNA vaccines Edible vaccines Problems with vaccine production and use EUKARYOTIC CELL-BASED DEFENSES AGAINST VIRUS REPLICATION Interferon Induction of interferon The antiviral state Measurement of interferon activity Other cellular defenses against viral infection Small...

Introduction The Impact of Viruses on Our View of Life

The effect of virus infections on the host organism and populations - viral pathogenesis, virulence, and epidemiology The interaction between viruses and their hosts Examples of the impact of viral disease on human history Examples of the evolutionary impact of the virus-host interaction Viruses have a constructive as well as destructive impact on society Viruses are not the smallest self-replicating pathogens

Pulse labeling of viral proteins at different times following infection

Study of the time of synthesis and nature of viral proteins in the infected cell requires the ability to distinguish virus-encoded proteins in a background of cellular ones, and to fractionate such viral proteins away from cellular components of the infected cell. Given the large amount of mass of the biological macromolecules contained in the cell, the process of viral protein or nucleic acid purification can be difficult and requires technical ingenuity. Although the detection of viral...

Viral and subviral diseases with long incubation periods

Most virus-induced diseases have low or only moderate mortality rates. Obviously, if a virus's mortality rate is too high, infection will kill off all the hosts so rapidly that a potential pool of susceptible individuals is lost. Exceptions to this rule do occur, however. Introduction of viral disease into a virgin population (perhaps due to intrusion into a novel ecosystem) can lead to high mortality. Prime examples are the spread of smallpox in Europe during the Middle Ages, and the...

A

Fig. 13.7 Control of eukaryotic transcription. (a) The availability of the transcription template is controlled by chromatin structure. This is generally a developmental process and condensation of chromatin into heterochromatin is often essentially irreversible in a differentiated cell. Such condensed chromatin is completely transcriptional silent and contains unacetylated histones and methylated DNA. Euchromatin is more loosely organized with acetylated histones in such regions genes are...

Loss of contact inhibition of growth and immortalization of primary cells

Immortalized B lymphocytes are but one example of cells available in the laboratory that have properties intermediate between the two extremes of continuous cell lines and primary cells. These cell types have undergone transformation and have at least some of the properties of tumor cells. Culturing primary cells for long periods can generate transformed cells. During the time in culture, there is a random accumulation of mutations that alter a critical number of growth control genes encoded by...

Rabies where is the virus during its long incubation period

Rabies and its transmission by the bite of infected animals to other animals and humans are well known in almost all human cultures. The disease and its transmission were carefully described in Arabic medical books dating to the Middle Ages, and there is evidence of the disease in classical times. One of the puzzles of rabies virus infection is the very long incubation period of the disease. This long period plays an important role in the mechanism of spread, and it is clear that animals (or...

The Innate Immune Response Early Defense Against Pathogens

When a virus infects an immunologically nai've host, one might expect that initially the odds are in favor of the virus. After all, most viruses have relatively short replication cycles, resulting in the rapid release of hundreds of new virions from a single cell. While the body immediately starts mounting specific antibody and cellular immune responses, it takes time for enough virus-specific B and T cells to accumulate in high enough numbers (even locally) to destroy infected cells, and to...

Animal virus entry into cells the role of the cellular receptor

Animal viruses must enter the cell in an appropriate manner through a complex plasma membrane composed of a lipid bilayer in which membrane-associated proteins float in the upper or lower surface (Fig. 6.1). Some integral membrane proteins form pores (channels) in the membrane for transport of ions and small molecules. Other proteins project from the cell's surface and are modified by the addition of sugar residues (glycosylation). Such glycoproteins serve many functions, including mediating...

Acute infections followed by virus clearing Colds and respiratory infections

Cold viruses (rhinoviruses, adenoviruses, and coronaviruses) are spread as aerosols. Infection is localized within the nasopharynx, and recovery involves immunity against that specific virus serotype. The vast array of different cold viruses and serotypes ensures that there will always be another one to infect individuals. Although generally these types of respiratory diseases are mild, infection of an immune-compromised host or a person having complications due to another disease or advanced...

A mouse model for studying poxvirus infection and spread

Many of the models developed for the study of viral pathogenesis involve the use of mice. These animals have an excellent immune system, can be infected with many viruses adapted from human diseases, and are relatively inexpensive to use. Frank Fenner's studies on the pathogenesis of mouse pox carried out in the 1950s provided a classic model for experimental study of viral pathogenesis. Although smallpox virus is extinct in the wild, the recent realization that smallpox has been extensively...

Analysis of viral capsids that do not contain equimolar numbers of proteins

Most viruses that encode more than a few proteins in their genomes (e.g., adenovirus and herpesviruses) have capsids that contain proteins in vastly different molar amounts. The adenovirus capsid is shown in Fig. 11.5. A number of proteins within the capsid are not visible in the figure these include core proteins and hexon-associated proteins. An example of an SDS gel fractionation for adenovirus is also shown in Fig. 11.5. The penton base protein, which is only found at the 12 vertices of the...

Questions For Chapter

1 You have diluted a 1-ml sample of virus stock by taking 100 ll from the stock solution and adding to it 0.9 ml of buffer. You then take 10 ll of this dilution and dilute it into 1 ml. You then infect two plates that contain 105 cells each with 100 ll. One plate had 25 plaques while the other had 29 plaques. What was the titer in the original stock 2 One milliliter of bacterial culture at 5 X 10s cells ml is infected with 109 phages. After sufficient time for more than 99 adsorption, phage...

Stages of virusinduced pathology

Pathogenesis can be divided into stages from initial infection of the host to its eventual full or partial recovery, or its virus-induced death. A more or less typical course of infection in a vertebrate host is shown schematically in Fig. 2.3. Although individual cases differ, depending on the nature of the viral pathogen and the immune capacity of the host, a general pattern of infection would be as follows Initial infection leads to virus replication at the site of entry and multiplication...

Virusmediated cytopathology changes in the biochemical properties of cells

Virus infection leads to specific changes in biochemical processes of the cell. Some viruses, such as HSV and poliovirus, specifically inhibit cellular protein synthesis. The mechanism for such inhibition is complex and differs for different viruses. Viral infection also can lead to specific inhibition of cellular mRNA synthesis. Gross inhibition of cellular macromolecular metabolism Fig. 10.4 HSV-induced changes in the properties of actin microfilaments of a cultured monkey fibroblast. The...

Herpesvirus Replication And Latency The herpesviruses as a group

The herpesviruses are extremely successful enveloped DNA viruses. They have been identified in all vertebrate species studied, and extend into other classes of the animal kingdom (oysters, for example). Their replication strategy involves a close adaptation to the immune defense of the host, and it is possible that their evolutionary origins as herpesviruses lie in the origins of immune memory. Eight discrete human herpesviruses are known at this time each causes a characteristic disease. Many...

Singlestranded DNA bacteriophage OX174 packages its genes very compactly

The gene packaging of bacteriophage OX174 suggests that genomic size compression offers distinct advantages in the prokaryotic world, also. This icosahedral virus has a structure very similar to that of adenovirus, but with shorter fibers. It contains a circular ssDNA genome approximately 3.4 kb long. Upon infection of a bacterial cell, the ssDNA genome is converted into dsDNA. This has been termed the replicative intermediate or replicative form (RF), but is quite unlike the complex...

DNA viruses infecting vascular plants

While DNA viruses infecting vascular (i.e., higher) plants might be expected to display genetic variability equivalent to that seen within animal and bacterial viruses, they do not appear to. The reason for this is that plant viruses must traverse a relatively thick and dense cell wall to approach and breach the plant cell's plasma membrane. Although at least one algal virus can insert its genome like bacterial viruses inject genomes, apparently the dimensions of the vascular plant's cell wall...

Replication of parvoviruses

The parvoviruses are very small, nonenveloped, icosahedral viruses. Two of the three known groups infect warm-blooded animals while the third group has members that infect insects. The parvovirus capsid diameter is 26-30 nm, significantly smaller than the polyomaviruses even though the viral genome is approximately 5 kb long. The virus is able to package the genome into such a small virion because the virus encodes only a single DNA strand. Interestingly, many parvoviruses can package the DNA...

The adenovirus replication cycle Early events

Adenovirus enters the cell via receptor-mediated endocytosis in a manner analogous to that of papillomaviruses. Cellular receptors interact with the virion fiber proteins to initiate infection. Adenovirus DNA with a specific terminal protein bound to each 5' end is released into the nucleus where it associates with cellular histones. In order to initiate gene expression, adenovi-ruses must stimulate the infected cell to transcribe and replicate its genes. This is accomplished by expression of...

Physical properties of adenovirus

Adenoviruses have complex icosahedral capsids whose proteins are not present in equimolar amounts (see Fig. 11.5), with projecting spikes or fibers at the 12 vertices (pentons). The viral genome is encapsidated with core protein that acts a bit like histone to provide a chromatin-like structure that is condensed in the interior of the nucleocapsid. The genome of adenoviruses is linear with specific viral protein (terminal protein) at the 5' ends. The genome is about 30,000 base pairs, and the...

Replication Of Adenoviruses

The adenoviruses comprise a large group of complex icosahedral, nonenveloped viruses of humans and other mammals. In humans, they generally are associated with cold or mild flu-like respiratory diseases, but some serotypes also are associated with gastrointestinal upsets. While adenoviruses are not at all closely related to the papovaviruses, they share with them a long replication cycle due to the need to stimulate and utilize many cellular functions to carry out virus replication. They also...

Replication of papillomaviruses

Cell transformation by SV40 appears to be a laboratory phenomenon, and many of the tumors caused by polyomaviruses can be thought of as dead-end artifacts of virus infection. In such infections, persistence appears to be due to the stability of histone-associated viral genomes in nonrep-licating cells marked by occasional episodes of low level viral replication as a result of an immune crisis or other events that lead to changes in the transcriptional environment of the host cell. By contrast,...

Replication of SV40 virus the model polyomavirus

Sv40 Genome Map

The polyomaviruses have genomes of approximately 5000 base pairs. Capsids are made up of three proteins, usually called VP1, VP2, and VP3. Polyomaviruses can cause tumors in animals and can transform the growth properties of primary cells in culture, especially the cells from animals different from the virus's natural host (see Chapter 10, Part III). Polyomaviruses also stay persistently associated with the host, often with little evidence of extensive pathology or disease. Although these...

Papovavirus Replication

The term papovavirus stands for papilloma, polyoma, vacuolating viruses. Actually, members of the group fall into two distinct families the papillomaviruses and polyomaviruses. These two groups are similar regarding icosahedral capsids, circular genomes, and the ability to remain associated with the host for long periods, as well as their requirement to specifically alter cell growth in the host cell's response to neighboring cells for virus replication. They differ in genome size and in many...

Dna Viruses Express Genetic Information And Replicate Their Genomes In Similar Yet Distinct Ways

Given that DNA is the universal genetic material of cells, it is not particularly surprising that viruses utilizing DNA as their genome comprise a significant proportion of the total number of known viruses. It also is not particularly surprising that such viruses will often use a significant proportion of cellular machinery involved in decoding and replicating genetic information encoded in double-stranded (ds) DNA, which is, after all, the stuff of the cellular genome. While it might be...

Chapter

DNA VIRUSES EXPRESS GENETIC INFORMATION AND REPLICATE THEIR GENOMES IN SIMILAR, YET DISTINCT, WAYS Replication of SV40 virus - the model polyomavirus The SV40 genome and genetic map Abortive infection of cells nonpermissive for SV40 replication Replication of papillomaviruses The HPV-16 genome Physical properties of adenovirus Capsid structure The adenovirus replication cycle Early events Adenovirus DNA replication Late gene expression VA transcription and cytopathology Transformation of...

Prions

As noted earlier, HDV utilizes an envelope borrowed from a helper virus, and itself encodes only one gene product. Pathogenic and nonpathogenic plant viroids are able to propagate their genomes without encoding capsid or any other protein. Prions form a logical limit to how simple a pathogen's structure can be. Prions are infectious agents that do not appear to have nucleic acid genomes Unfortunately, this simplicity does not mean that investigation of the problem of prion pathogenicity is...

Viroids

Plant viroids are infectious agents that have no capsid and have an RNA genome that encodes no gene product they do not require a helper for infectivity. Potato spindle tuber viroid is the prototype of this class of agents. The viroids are covalently closed, circular, single-stranded RNAs, 246-375 nucleotides long, whose sequence is such that base pairing occurs across the circle, as shown in Fig. 15.13. As a result, these agents have the form of a dsRNA rod with regions of unpaired loops....

Hepatitis delta virus

As briefly outlined in Chapter 4, Part I, HDV appears to be absolutely dependent on coinfec-tion with hepatitis B virus (HBV) for spread. Despite this, there are a significant number of cases where it can be inferred that an individual was infected with HDV without any evidence of active or prior HBV infection. The HDV genome, shown in Fig. 15.12, has very significant similarities with plant viroid RNAs It is difficult to come up with a convincing scenario that explains how a plant pathogen...

Reovirus replication cycle

Image Replication Cycle Reovirus

Some features of the replication of reovirus in the infected cell are shown in Fig. 15.11. After attachment and entry into the host cell cytoplasm via receptor-mediated endocytosis, reovirus particles are partially uncoated, leaving behind an inner-core subviral particle. This subviral particle contains the 10 genome segments and transcriptional enzymes. Production of mRNAs occurs by the copying of one strand of each duplex genome into a full-length strand. The mRNAs are capped and methylated...

Reovirus structure

A schematic of the virion and the protein coding strategy of the genomic segments is shown in Fig. 15.10. These genome segments of the reo-viruses are packaged into an icosahedral capsid that consists of two - or in some members, three - concentric shells, each having icosahedral symmetry. The capsid is made up of three 1C o3 complex (outer capsid) 11 o2 complex (core) 27 aNS (366 aa) 73 32 C13 (365 aa) 69 Fig. 15.10 The 60-nm-diameter human reovirus with...

Viruses With Doublestranded Rna Genomes

The family Reoviridae contains nine distinct genera with infectious agents specific for vertebrates (reoviruses and rotaviruses), invertebrates (cytoplasmic polyhedrosis virus), and plants (wound tumor virus). Members of this family have genomes consisting of 10, 11, or 12 segments of double-stranded (ds) RNA. There is a group of bacterial viruses, many infecting Bacillus subtilis, that also contains segmented, double-stranded genomes. The replication strategy employed by these viruses must...

Bunyaviruses

In terms of the number of members, the bunyavirus family (Bunyaviridae) is one of the largest known, with well over 300 serologically distinct viruses. The family itself consists of five separate genera, as listed in Table 15.2. Most members of this diverse family are arboviruses, being transmitted by mosquitoes, ticks, sandflies, or thrips. The hantaviruses, however, are vectored by rodents. Bunyaviruses all have tripartite, negative-sense RNA genomes. As outlined in Fig. 15.8, the enveloped...

Wwvw

Fig. 15.6 An outline of the replication cycle of influenza. Following virus attachment to its cellular receptor(s) and endocytosis, the envelope fuses with vesicular membrane. The released ribonucleoprotein (RNP) capsid segments, each containing a specific negative-sense genomic segment, migrate to the nucleus where transcription of positive-sense RNA takes place using virion-associated transcriptase. The transcription and formation of mRNA require the snatching or stealing of caps of nascent...

Influenza A epidemics

Flu is generally considered to be a mild disease, but influenza can be a major killer of the aged and the immune compromised. Even though the body mounts a strong and effective immune reaction to influenza infections, and the individual is immune from reinfection upon recovery, the virus is able to mount periodic epidemics in which prior immunity to related strains is no protection. The solution to this apparent enigma is found in the broad host range of influenza A and the unique ability of...

Generation of new flu nucleocapsids and maturation of the virus

An abbreviated schematic of the influenza A virus replication cycle in a susceptible cell is shown in Fig.15.6. Infection is initiated by virus attachment to cellular receptors followed by receptor-mediated endocytosis. The separate RNPs with their negative-sense genome segments are transported to the nucleus where viral mRNA synthesis begins. Viral mRNA synthesis requires the activity of at least two influenza virus polymerase sub-units, PB1 and PB2. PB1 has active sites that bind the...

Involvement of the nucleus in flu virus replication

Despite some general similarities with VSV in transcription of the genomic negative-sense strands of influenza virus to generate mRNA, there are important differences in the overall replication process. A major difference is that influenza virus mRNA synthesis and genome replication require the cell's nucleus. There are two readily apparent reasons for this. First, flu replicase cannot cap mRNA therefore, each flu virus mRNA generated has to use a cellular mRNA cap as a primer. Synthesis of...

Influenza Viruses Negativesense Rna Viruses With A Multipartite Genome

The negative-sense RNA viruses with monopartite genomes share enough similarities to allow their grouping into a superfamily, the Mononegavirales. By contrast, the three major groups (orthomyxoviruses, bunyaviruses, and arenaviruses) have not been convincingly grouped into a single superfamily. Despite this, the negative-sense RNA viruses with multipartite genomes also share some features in replication strategies and genomic sequence. Due to periodic and frequent spread through the human...

Filoviruses and their pathogenesis

In 1967 some medical researchers working with Ugandan African green monkeys (an important experimental animal and source of cultured cells) in Marburg, Germany, and in Yugoslavia contracted a severe hemorrhagic fever that was highly infectious to clinical staff via blood contamination. A total of seven of 25 of these workers subsequently died of the infection. Since its first appearance, the infectious agent, termed Marburg virus, has caused several outbreaks of hemorrhagic fevers with similar...

Paramyxoviruses

Paramyxoviruses have large genomes (approximately 15,000 bases) and their replication cycle is reminiscent of that described for rhabdoviruses. One notable exception is that several (including mumps) generate mRNA that has been edited by the addition of extra G nucleotides as the mRNAs for specific genes are expressed. The addition of these nucleotides is apparently accomplished by a stuttering step similar to that involved in the addition of polyA residues at the end of transcripts. This...

T t

An abbreviated outline of the flavivirus replication cycle can be inferred from the genetic and structural map shown in Fig. 14.5, and taken from work with yellow fever virus. The flavivirus genome is over 10,000 bases long, and unlike poliovirus, it is (i) capped at the 5' end and (ii) not polyadenylated at the 3' end. Like poliovirus, the large ORF is translated into a single precursor protein that is cleaved by integral proteases into individual proteins. Some of these cleavage steps are...

Nonspecific methods of introducing viral genomes into cells

Clearly, the process of infection of a cell by a virus essentially involves the efficient insertion of the viral genome into an appropriate location within the cell so that viral genes can be expressed. The fact that viruses can be internalized into plant cells without the benefit of receptors suggests that other methods for the introduction of viral genomes can take place, if only rarely. In the laboratory for example, cells can be made permeable by chemical or physical methods so that they...

Entry of virus into plant cells

A plant cell's special architecture, namely the presence of a rigid and fairly thick cell wall, presents a unique challenge for virus entry. Initial entry into the plant cell must take advantage of some break in integrity of the cell wall. Apparently, when the virus enters such a break and becomes situated in close proximity to the plant cell's plasma membrane, it can enter the cell without interaction with specific receptors. Breaks or lesions in the plant cell's wall are most often produced...

The Features Of A Virus

Viruses are small compared to the wavelength of visible light indeed, while the largest virus can be discerned in a good light microscope, the vast majority of viruses can only be visualized in detail using an electron microscope. A size scale with some important landmarks is shown in Fig. 5.1. Virus particles are composed of a nucleic acid genome or core, which is the genetic material of the virus, surrounded by a capsid made up of virus-encoded proteins. Viral genetic material encodes the...

The Adaptive Immune Response And The Lymphatic System

Endogenous Antigen Presentation

The human lymphatic system shown in Fig. 7.2 is part of the general circulatory system and plays a critical role in developing the immune response to the presence of foreign proteins in the body. When any protein that is not part of the vast protein repertoire making up the vertebrate host is presented to the immune system by an antigen-presenting cell (APC), both B-cell immunity (humoral immunity) and T-cell immunity (cell-mediated immunity CMI ) are mobilized. Such a foreign protein is...

Questions For Chapter 15

1 What features of the viral replication cycle are shared by measles virus, vesicular stomatitis virus, and influenza virus 2 When the genomes of negative-sense RNA viruses are purified and introduced into cells that are permissive to the original intact virus, what will occur 3 The Rhabdoviridae are typical negative-sense RNA viruses and must carry out two types of RNA synthesis during infection transcription and replication. Briefly describe each of these modes of viral RNA synthesis. 4 Sin...

Eukaryotic Cellbased Defenses Against Virus Replication Interferon

The clonal selection of antibody-producing B cells and effector T cells provides an exquisitely sensitive means for the infected host to specifically deal with invading microorganisms and viruses, and to eliminate virus-infected and thus damaged cells. However, it does take time for an effective defense to be mounted. There are more rapid if less specific defenses available locally. As briefly discussed in Chapter 7, these include the action of proteins with broad-spectrum antipathogen...

The Science Of Virology

The study of viruses has historically provided and continues to provide the basis for much of our most fundamental understanding of modern biology, genetics, and medicine. Virology has had an impact on the study of biological macromolecules, processes of cellular gene expression, mechanisms for generating genetic diversity, processes involved in the control of cell growth and development, aspects of molecular evolution, the mechanism of disease and response of the host to it, and the spread of...

Visualization and Enumeration of Virus Particles

Transmission Electron Microscope

Using the electron microscope to study and count viruses Counting (enumeration) of virions with the electron microscope Atomic force microscopy - a rapid and sensitive method for visualization of viruses and infected cells, potentially in real time Indirect methods for counting virus particles QUESTIONS FOR CHAPTER 9 Most viruses are submicroscopic physical particles, and while the largest can be discerned in an ultraviolet (UV)-light microscope, detailed visualization requires other methods....

Bacterial Antiviral Systems Restriction Endonucleases

Bacterial cells do not have the ability to produce antibodies or IFN as do animal cells. However, they have evolved mechanisms through which viral infections can be aborted, or at least limited. Bacterial restriction is the most common types of antiviral defense. The discovery of bacterial restriction systems not only led to a basic understanding of bacterial viral interactions but also provided one of the most critical set of tools used in modern molecular biology and biotechnology restriction...

Control And Dysfunction Of Immunity

Secondary response (second inoculation of antigen) Fig. 7.7 Immune memory. The first exposure to an antigen results in the primary response, which occurs after a week or so. During this time, maturation of immune-reactive cells is taking place. Once the primary response occurs, antibody and reactive T and B cells decline to a low level. Upon restimulation with the same antigen, the memory lymphocytes are rapidly mobilized and a more intense and more rapid immune response follows. Fig. 7.8 The...

The replication of the prototypical alphaherpesvirus HSV The HSV virion

All herpesviruses possess similar enveloped icosahedrons. The envelope of HSV contains 10 or more glycoproteins. The matrix (called the tegument for obscure reasons) lies between the envelope and the capsid and contains at least 15 20 proteins. The capsid itself is made up of six proteins the major one, VP5, is the 150,000-dalton major capsid protein. VP5 is also called Ul19 for the position of its gene on the viral genetic map. A computer-enhanced model of the HSV capsid structure is shown in...

The poliovirus capsid a virion with equimolar capsidproteins

It is relatively easy to determine that the poliovirus capsid is made up of just four proteins, and that the four capsid proteins VP1, VP2, VP3, and VP4 are present in equimolar amounts in the capsid. Groups of five copies of each protein are arranged at each of the 12 vertices of the icosahedral capsid see Chapters 5 and 15 . If the proteins are uniformly labeled with radioactive amino acids, more radioactivity will be in each large polypeptide chain than in each small one. A gel fractionation...

Rate zonal sedimentation and gel electrophoresis for measuring viral genome size

In contrast to DNA molecules, molecules of single-stranded ss RNA, as found in the genomes of many RNA viruses, are susceptible to chemical degradation at relatively mild pH ranges lt 3 and gt 9 . Further, ribonucleases that readily degrade RNA are notoriously difficult to inactivate and are often excreted by bacteria and fungi, which can contaminate laboratory reagents. Indeed, a very potent ribonuclease finger nuclease is found in sweat and is carried on the Fig. 11.9 Use of a method similar...

Replication of vesicular stomatitis virus a model for Mononegavirales

Stomatitis Virus

Infection of humans with naturally occurring strains of rabies virus leads to fatal diseases. This and other factors make this virus difficult and dangerous to work with indeed, much of the work on it is carried out in a few very isolated laboratories in the United States, including Plum Island in Long Island Sound. By contrast, the closely related rhabdovirus vesicular stomatitis virus VSV is one of the most carefully studied extant viruses. Its replication strategy forms a valid model for the...

Replication Of Negativesense Rna Viruses With A Monopartite Genome

There are four families of negative-sense RNA viruses that package their genomes as a single piece of RNA Rhabdoviridae, Paramyxoviridae, Filoviridae, and Bornaviridae. They all share some similarities of gene order and appear to belong to a common superfamily or order Mononegavirales. Interestingly, despite genetic relatedness of these viruses, they do not share a common shape, although all are enveloped. Also, the rhabdovirus family contains several members that infect plants. Is this a...

Regulated translation of bacteriophage mRNA

There is a major difference in the way protein synthesis occurs on bacterial ribosomes as compared to eukaryotic ribosomes, and this leads to a significant difference in the way expression of viral-encoded protein is controlled. As discussed in Chapter 13, bacterial ribosomes can initiate translation at start sites in the interior of bacterial mRNA. This means that a bacterial mRNA molecule with several ORFs can be translated independently into one or all of the proteins. In an RNA...

Replication Of Bacteriophage With Rna Genomes

The great majority of well-characterized RNA bacteriophages have linear, single-stranded, positive-sense genomes enclosed within small, icosahedral capsids. These phages grouped together as the Leviviridae include the male bacteria-specific phage QP, MS2, and R17, which attach to the bacteria's F pili. In broad outline, the replication process of these RNA-containing bacteriophages follows that described for eukaryotic viruses. Infection begins with a translation step, and replication of the...

Viruses with three genome segments

Brome grass mosaic virus has three separate RNA genome strands 3.2 kb, 2.8 kb, and 2.1 kb contained in three separate icosahedral particles. Again, since all three genome segments are required for infection, cells must receive one of each of the particles. Each of the capped genome segments is translated into a protein. These products include the 94-kd viral replicase, a 109-kd capping enzyme, and a 32-kd cell-to-cell movement protein. In addition, one of the RNAs is transcribed into a...

Replication Of Plant Viruses With Rna Genomes

A large number of plant viruses contain RNA genomes, and many of the early discoveries in virology were accomplished with plant viruses. The discovery of viruses as specific infectious particles at the end of the nineteenth century focused on work to elucidate the cause of tobacco mosaic disease, culminating in the first description of the tobacco mosaic virus TMV . This virus took center stage for a number of important early events in biochemical virology, including the first crystallization...

Positivesense Rna Viruses Encoding More Than One Translational Reading Frame

Coronavirus Replication Review

A positive-sense RNA virus that must regulate gene expression while infecting a eukaryotic host faces a fundamental problem The eukaryotic ribosome cannot initiate translation of an ORF following translation of one upstream of it. While a positive-sense RNA virus genome could and some do contain more than one ORF, these ORFs cannot be independently translated at different rates during infection without some means to overcome this fundamental mechanistic limitation. One way to overcome the...

Picornavirus replication

Poliovirus Replication Cycle

Picornaviruses are genetically simple and have been the subject of extensive experimental investigation owing to the number of diseases they cause. Their name is based on a pseudoclassical use of Latin mixed with modern terminology pico small -RNA-virus. The replication of poliovirus the best-characterized picornavirus, and perhaps, best-characterized animal virus provides a basic model for RNA virus replication. Studies on poliovirus were initiated because of the drive to develop a useful...

Replication Of Positivesense Rna Viruses Whose Genomes Are Translated As The First Step In Gene Expression

The first step in the infectious cycle of this group of positive-sense RNA viruses also called positive strand viruses leading to expression of viral proteins is translation of viral protein. If the virion genomic RNA is incubated with ribosomes, transfer RNA tRNA , amino acids, ATP, GTP, and the other components of an in vitro protein synthesis system, protein will be synthesized. Further, if virion RNA is transfected into the cell in the absence of any other viral protein, infection will...

Rna Viruses General Considerations

By definition, RNA viruses use RNA as genetic material and thus, must use some relatively subtle strategies to replicate in a cell since the cell uses DNA. Ultimately, to express its genetic information, any virus must be able to present genetic information to the cell as translatable mRNA, but the way this happens with RNA viruses will depend on the type of virus and the nature of the encapsidated RNA. According to Watson Crick base-pairing rules, once the sequence of one strand of either RNA...

Replication of Positivesense RNA Viruses

RNA VIRUSES - GENERAL CONSIDERATIONS A general picture of RNA-directed RNA replication REPLICATION OF POSITIVE-SENSE RNA VIRUSES WHOSE GENOMES ARE TRANSLATED AS THE FIRST STEP IN GENE EXPRESSION POSITIVE-SENSE RNA VIRUSES ENCODING A SINGLE LARGE OPEN READING FRAME The poliovirus genetic map and expression of poliovirus proteins The poliovirus replication cycle Picornavirus cytopathology and disease POSITIVE-SENSE RNA VIRUSES ENCODING MORE THAN ONE TRANSLATIONAL READING FRAME Two viral mRNAs...

Replication Patterns of Specific Viruses

Replication of Positive-sense RNA Viruses RNA Viruses - General Considerations Replication of Positive-sense RNA Viruses Whose Genomes are Translated as the First Step in Gene Expression Positive-Sense RNA Viruses Encoding a Single Large Open Reading Frame Positive-Sense RNA Viruses Encoding More Than One Translational Reading Frame Replication of Plant Viruses with RNA Genomes Replication of Bacteriophage with RNA Genomes Replication Strategies of RNA Viruses Requiring RNA-directed mRNA...

A general picture of RNAdirected RNA replication

With the exception of retroviruses and some unusual viruses related to viroids, single-stranded ss RNA virus genome replication requires two stages these are shown in Fig. 14.1 b . First, the input strand must be transcribed using Watson Crick base-pairing rules into a strand of complementary sequence and opposite polarity. Replication occurs as a fuzzy, multi-branched structure. This complex, dynamic structure contains molecules of viral transcriptase replicase , a number of partially...

Problems

1 The table below shows the properties of the genomes of three different viruses. The data were obtained as follows Nuclease sensitivity was measured by the ability of deoxy-ribonuclease DNase or ribonuclease RNase to destroy the genome a means sensitivity . The ability of the genome to act as mRNA was tested by incubating it in a cell-free system. If amino acids were incorporated into protein, the data are shown as a . Finally, the virus particles were tested for the presence of a virion...