Virus dsRNA

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,... 

In eukaryotes, DNA is generally double-stranded (dsDNA) and RNA is generally single-stranded (ssRNA). Exceptions occur in certain viruses, some of which have ssDNA genomes and wime of which have dsRNA genomes.. ... 

FIGURE 10.10 RNAi sequence. First the vims approaches and attaches itself to the cell wall (A). The virus injects double-stranded RNA (B) into the cell cytoplasm. The dicer attacks the dsRNA, breaking it into smaller units (C and D). These smaller units are then acted on by RISC, forming single-stranded viral RNA (E), which are rendered incapable of forming their own protein by attachment to a complement contained within the cell s own single-stranded RNA (F). 

Naitow, H., et al. (2001). Purification, crystalhzation and preliminary X-ray analysis of L-A a dsRNA yeast virus. /. Struct. Biol. 135,1-7. 

Interferons are natural proteins produced by the cells of the immune system in response to challenges by foreign agents such as viruses, parasites and tumor cells. Interferons assist the immune response by inhibiting viral replication within host cells. There are three major classes of interferons, interferon type I, interferon type II and interferon type III. They bind to a differen cell surface receptor complexes. The type I interferons in humans are IFN-o , IFN-jS and IFN- >. IFN-y is human interferon type II. All classes of interferon are important in fighting RNA virus infections and endogenous interferons are secreted when abnormally large amounts of dsRNA are found in a cell. 

While most plant viruses contain dsRNA, the geminiviruses,458 which cause a number of plant diseases, contain single-stranded DNA. The virus particle consists of a fused pair of incomplete icosahedra, evidently containing a single 2500-bp DNA strand. Replication may require coinfection with two virus particles of differing sequence. 

The binding of interferons to their receptors induces a rapid increase in the transcription of particular genes and synthesis of corresponding proteins.196 202 One of the proteins induced is a double-stranded RNA-activated 2 -5 A synthase, which polymerizes ATP to a series of 2 -5 linked oligonucleotides containing triphosphates at the 5 termini.202-204 Double-stranded RNA is uncommon except in replicating viruses, and it is thought that the activation by dsRNA is related to establishment of an antiviral state. Another interferon-induced enzyme is the small subunit of eukaryotic protein synthesis initiation factor eIF-2. 

No crystallographic structure is currently available for GPV-type single-shelled dsRNA virus capsids. Two cryo-EM reconstructions have been performed, which reveal much the same architecture as the orthoreovirus core a single layer with turrets at the 5-fold vertices, statistically ordered layers of dsRNA, and a clamping protein at 2-fold axes (Hill et al, 1999 ... 

Zhang et al, 1999). The layers of dsRNA have also been detected by SAXS (Harvey et al., 1981). As with BTV and orthoreovirus, a 120-subunit surface forms the first (and here only) layer, a capsid geometry that was previously unknown and that appears to be ubiquitous among reoviruses. The virus is occluded within a crystal of the viral protein polyhedrin (Payne and Mertens, 1983), which dissolves in the alkaline pH of the insect gut, releasing infectious viruses. Occlusion within a robust crystal lattice provides a communal solution to the need for protection provided in other reoviruses by outer viral layers. 

Fig. 6. Resolution assessments, (a) Differential phase residual method based on the 45 phase difference criterion used in the 8.5-A resolution (indicated by arrow) structure of the herpesvirus capsid (Zhou et al., 2000). (b) Fourier shell correlation method based on the 0.5 Fourier shell correlation coefficient criterion used in the assessment of effective resolution of the rice dwarf virus (RDV) structure at 6.8 A (Zhou et al, 2001). The imperfect FSC value (<1.0) is partly due to the presence of nonicosahedrally ordered dsRNA genomes within the RDV virions. [Adapted from Zhou et al. (2000, 2001), with permissions from the publishers.]...

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