Single-Stranded RNA Viruses

Many of the ssRNA viruses have icosahedral symmetry. X-ray crystallographic structures of several of these viruses have been determined. In some of these structures, a significant portion of the genome is ordered. 

The satellite ssRNA viruses are a group of ssRNA icosahedral viruses, which are the satellites to certain plant viruses (Pritsch and Mayo, 1989). Satellite tobacco necrosis virus (STNV), a satellite virus to tobacco necrosis virus, was in fact one of the first icosahedral virus structures to be determined by X-ray crystallography (Liljas et al, 1982). In more recent years, two other satellite plant viruses, satellite tobacco mosaic virus (STMV) (Larson et al, 1993, 1998) and satellite panicum mosaic virus (SPMV) (Ban and McPherson, 1995), have been determined. These are perhaps the simplest and smallest icosahedral viruses whose structures have been determined by X-ray crystallography. Of relevance to our discussion is the structure of STMV determined to 1.8-A resolution, which shows extraordinary details about genome organization (Larson et al, 1998 Larson and McPherson, 2001). 

The capsid of STMV, 170 A in diameter, with 60 monomeric subunits, is organized on a T=1 icosahedral lattice. The capsid encloses an ssRNA genome of 1059 bases. The 159-amino acid-long capsid protein exhibits a canonical antiparallel 8-stranded /3-sandwich fold, with the N-terminal 36 residues in highly extended conformation facing the interior of capsid. About 45% of the genome is seen in the electron density map along with 

The X-ray crystallographic structures of nodaviruses have unraveled a unique role for the double-helical segments of the encapsidated RNA in 

During its infection cycle, for a productive infection to occur, the virus must release the encapsidated genome at an appropriate location inside the host cell. The genome release is often associated with the disassembly 

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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... 

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). 

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. 

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 chart of events during the replication of negative single-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... 

E. Specific Recognition of the Genome in Single-Stranded RNA Viruses.. 227... 

F. Genome Structure in Helical Single-Stranded RNA Viruses. 228... 

T = 3 single-stranded RNA virus, as icosahedral single-stranded RNA viruses, 224... 

Recently, another genome, GBV C (ca. 9,200 nucleotides), was identified by means of PCR. (539, 549) It is defined as a single-stranded (+) RNA virus and forms a separate species within the flaviviridae family. It seems that the original serum of GB contained no (or no more) GBV A, GBV B or GBV C RNA thus the above mentioned surgeon s hepatitis remains unclarified with regard to the causative virus type. In the meantime HCV could be differentiated into five subtypes la, lb, 2a, 2b and 3a. 

Nonpolio enteroviruses are unenveloped single-strand RNA viruses. Commonly, the incidence of enteroviral encephalitis peaks... 

Another emergent viral hepatitis is that causes by E virus, a single stranded RNA virus, which is endemic in many areas like North America and Asia. It can be transmitted via the faecal-oral ronte, water and also food. This virus causes acute hepatitis and it is important to distinguish it from other kind of viral hepatitis. The pathogenesis of hepatitis E is not well known and the diagnosis is actually mainly serological even if a molecular method represents that preferable to be developed. 

HIV is a single-stranded RNA virus that contains a virally encoded DNA polymerase enzyme, reverse transcriptase (RT). The HIV RT is the enzyme responsible for transcribing viral RNA into DNA, a cytoplasmic event. Following reverse transcription, the HIV DNA enters the cell nucleus and, through the action of another viral enzyme (integrase), is incorporated into the host cell genome. It is this event, the incorporation into host DNA that makes HIV infection a chronic, lifelong disease, because each time the lymphocyte is activated and the DNA transcribed and translated, new HIV virions are created and released. 

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