Stranded RNA Viruses

Unique Organization of Capsid Layer That Surrounds the Genome 

In the several members of Reoviridae, following cell entry the mature virion, which generally is transcriptionally incompetent, is converted into a transcriptionally competent unit by the removal of outer capsid layer (s). In rotavirus, for instance, the mature particles have three concentric capsid layers (Prasad and Estes, 2000) (Fig. 3 see Color Insert). Following 

Although the precise organization of the genome that can facilitate repeated cycles of transcription remains to be elucidated, structural studies have provided some useful hints. Cryo-EM studies on rotavirus 

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The N-terminal part of the tomato bushy stunt virus polypeptide chain (the R-segment in Figure 16.8) is disordered in all the subunits. As in the core of many other single-strand RNA viruses this region of the polypeptide chain... 

Viral Proteases. Figure 1 Role of virally encoded proteases in the replication cycle of a retrovirus (HIV, part a) and of a (+)-strand RNA virus (HCV, part b). The numbers correspond to the following steps in the infectious cycle ... 

The infectious cycle of a (+)-strand RNA virus such as the hepatitis C virus differs by the fate of the viral RNA genome in the infected cell. Upon entry into the cell, the HCV genome is used as a messenger RNA to drive the synthesis of a large polyprotein precursor of about 3,000 residues [2]. The structural proteins are excised from the precursor by host cell signal peptidase. 

In contrast to retroviruses, proteolysis is an early event in the replication cycle of (+)-strand RNA viruses and both protease and polymerase inhibitors can be expected to halt the propagation of infectious viral particles from already infected cells. 

HCV is a small enveloped single-stranded RNA virus belonging to the Flaviviridae family and Hepacivirus genus [12]. Other Flaviviridae members include the flaviviruses such as yellow fever virus, and pestiviruses, which are responsible, for example, for bovine viral diarrhea [13]. The most closely related virus identified to date is GBV-B, which infects the tamarind, a new world monkey. GBV-B has also been tentatively classified as a Hepacivirus... 

Hepatitis C, first known as non-A, non-B hepatitis, is a blood-borne infection that is a single-stranded RNA virus belonging to the Flaviviridae family and the Hepacivirus genus.12 The... 

HCV is a single-stranded RNA virus of the Flaviviridae family. It has a 9.4-kb positive-sense genome encoding a polyprotein precursor of 3011 amino acids. Individual isolates of HCV consist of closely related yet heterogeneous populations... 

We have also noted in Section 5.8 that the RNA of the cell is generally in the single-stranded configuration. Interestingly, although single-stranded RNA viruses are more common, viruses are known in which the RNA is in the double-stranded form. 

Similarly, the case for monophyly is hard to sustain for the origin of multicomponent (segmented) RNA viruses (positive single stranded RNA viruses, e.g. tobravirus, cucumovirus and bromovirus) and plant bipartite DNA viruses (single stranded DNA viruses, e.g. geminivirus) where coinfection ( two for one ) is required for the production of new virions (see Summary in Shostak, 1999). 

Double-stranded RNA (dsRNA) in yeast, 26 451—452 Double-stranded RNA viruses, 3 135 Double-suction pumps, 21 60, 63 Double tipping pan vacuum filter, 11 352 Double titration method, 15 145 Double vacuum-arc remelting (VAR), in titanium sponge consolidation, 24 854 Double wall nanotubes (DWNT), 26 737 Double-wall tanks, 24 296 Doubly smart block copolymers,... 

Replication of Viral Nucleic Acid. In addition to producing molecules for the formation of new capsids, the virus must replicate its nucleic acid to provide genetic material for packaging into the capsids. The way in which this is done might vary. In positive-sense, single-strand RNA viruses, a polymerase translated from viral mRNA produces negative-sense RNA from the positive-sense template which is then repeatedly transcribed into more positive strands. 

There is a wide variety of vectors used to deliver DNA or oligonucleotides into mammalian cells, either in vitro or in vivo. The most common vector systems are based on viral [retroviruses (9, 10), adeno-associated virus (AAV) (11), adenovirus (12, 13), herpes simplex virus (HSV) (14)] andnonviral [cationic liposomes (15,16), polymers and receptor-mediated polylysine-DNA] complexes (17). Other viral vectors that are currently under development are based on lentiviruses (18), human cytomegalovirus (CMV) (19), Epstein-Barr virus (EBV) (20), poxviruses (21), negative-strand RNA viruses (influenza virus), alphaviruses and herpesvirus saimiri (22). Also a hybrid adenoviral/retroviral vector has successfully been used for in vivo gene transduction (23). A simplified schematic representation of basic human gene therapy methods is described in Figure 13.1. 

Double-Stranded RNA Viruses, Elsevier, Biomedical, New York... 

Yet again the conclusion can be drawn that all single-stranded RNA viruses are subject to similar restrictions with regard to information content. In nature there are no (single-stranded) RNA viruses whose replicative unit contains more than the order of 104 nucleotides. All larger viruses possess double-stranded nucleic acids or are composed of several... 

A neurotropic, enveloped and negative single-stranded RNA virus that persistently infects domestic animals (e.g. horses) causing behavioural and cognitive dysfunction. 

Flow of events during the replication of a positive-strand RNA virus. 

Liu, L., Botos, I., Wang, Y., Leonard, J.N., Shiloach, J., Segal, D.M. Davies, D.R., Structural basis of toll-like receptor 3 signaling with double-stranded RNA. Science 320 (2008) 379-381. Lund, J.M., Alexopoulou, L., Sato, A., Karow, M., Adams, N.C., Gale, N.W., Iwasaki, A., Flavell, R.A. Recognition of single-stranded RNA viruses by Toll-like receptor 7. Proc Natl Acad Sci... 

Nagasaki K, Tomaru Y, Katanozaka N, Shirai Y, Nishida K, Itakura S, Yamaguchi M (2004) Isolation and characterization of a novel single-stranded RNA virus infecting the bloom-forming diatom Rhizosolenia seti-gera. Appl Environ Microbiol 70 704-711... 

The hepatitis C virus was defined in 1989. Prior to this, hepatitis following blood transfusion that was not caused by hepatitis A or B was referred to as non-A, non-B hepatitis. HCV is a positive, single-stranded RNA virus of the Flaviviridae family. HCV can be subdivided into groups depending upon the genotype of the virus, which may be important in determining the severity of the disease and the response to treatment. It has been estimated that around 170 million people worldwide are infected with hepatitis C [15]. HCV is primarily transmitted... 

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