Stranded DNA Viruses

The dsDNA-containing bacteriophages are icosahedral virions composed of a single major capsid protein, sometimes although not always decorated with accessory proteins. They can be prolate, such as is the case 

The organization of the dsDNA within phage capsids has long intrigued 

Given the amount of pressure stored in the packaged DNA it is tempting to speculate that this might provide the driving force for entry of the DNA into the host cell (Smith et at, 2001). (Phages are not internalized during 

The adenovirus capsid is an icosahedral capsid that can be described as pseudo-T=25. The 12 pentameric vertices are each composed of 5 molecules of the penton bases, carrying a trimeric fiber. The 20 faces are composed of the 4 molecules of hexon protein, which itself is a trimer of the 967-residue-long polypeptide II. The crystal structure of the hexon has been solved and it reveals that the trimeric subunits are intimately intertwined, thus accounting for their observed stability. The capsid also 

Adenovirus contains a 35-kb dsDNA complexed with four adenovirus-encoded proteins (V, VII, m, and terminal), perhaps in a nucleosome-like arrangement (Burnett, 1997). The arrangement has been controversial, as it has been suggested that the nucleoprotein is arranged both with and without overall icosahedral symmetry. Cryo-EM data support the notion that there is perhaps a small degree of icosahedral symmetry enforced by the capsid lattice, but that there is no well-structured overall icosahedral symmetry within the core (Stewart et al, 1991). 

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Many bacterial viruses have genomes containing double-stranded DNA. Such viruses were the first bacterial viruses discovered, and have been the most extensively studied. With such a range of double-stranded DNA viruses, a wide variety of replication systems are present. In the present section, we discuss the best studied and most representative of the group, T4 and T7. The simpler, T7, will be discussed first. 

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). 

A dubious, but not uninteresting case can be made for mammalian herpesviruses, large double-stranded DNA viruses, which might have evolved from their mammalian hosts. Their nonstructural (enzymatic and control) viral proteins are similar to those of nonviral host proteins (McGeoch and Davidson, 1995), although recombination might also explain these similarities. 

Additional viruses that may prove of some use as future viral vectors include adeno-associated virus and herpes virus. Adeno-associated virus is a very small, single-stranded DNA virus its genome consists of only two genes. It does not have the ability to replicate autonomously and can do so only in the presence of a co-infecting adenovirus (or other selected viruses). 

Double-pulse ruby laser, 14 697-698 Double refraction, 14 675 Double salts, lanthanide, 14 633-634 Double-stranded DNA viruses, 3 135... 

Baculoviruses are members of a large group of double-stranded DNA viruses which only infect invertebrates, including insects. The restricted host range makes baculoviruses safer than mammalian expression systems. The most widely used baculoviruses are Autographa califor-nica nuclear polyhedrosis virus and the Bombyx mori nuclear polyhedrosis virus. The host cell most commonly used is Sf9, derived from the fall army worm Spodoptera frugiperda. 

Two types of DNA viruses have also been used in human gene therapy trials. Adenoviruses, double-stranded DNA viruses, can efficiently carry a larger gene into cells even if they are not dividing, but the genetic information does not become inserted into the cell s genetic material and the information may rapidly be lost. Adeno-associated virus vectors, made from small single-stranded... 

Adenovirus Features. Adenovirus is a nonintegrating double-stranded DNA virus that is packaged into an icosahedra structure consisting of seven different proteins. The vertices of the icosahedrons contain a penton base with a protruding... 

Canine parvovirus, first identified in 1978, is now endemic.455,456 Childhood fifth disease is also caused by a parvovirus.456,457 When these single-stranded DNA viruses infect cells a double-stranded replicative form of DNA arises by synthesis of the complementary negative strand alongside the original positive DNA strand. Many copies of the replicative form are then synthesized. The negative strands of the replicative forms serve as templates for synthesis of numerous new positive strands that are incorporated into the progeny viruses. The whole process may take only 20 minutes. Some parvoviruses are unable to reproduce unless the cell is also infected by a larger adenovirus. 

The duplex is a right-handed double helix with 10 bases per turn. The diameter of the helix is 20 A (2 nm) and the pitch is 34 A (3.4 nm). The sugar-phosphate backbone is on the outside of the helix, and the two antiparallel chains are connected by the hydrogen-bonded bases. The DNA in prokaryotes and eukaryotes is generally found in the duplex form, although there are some single-stranded DNA viruses. DNA is a very robust molecule in comparison with many proteins. The simple double-helical secondary structure is readily reassembled after denaturation, unlike the complex tertiary protein structures that can denature... 

Adeno-associated viruses A class of small, single-stranded DNA viruses that can insert their genetic material at a specific site on chromosome 19. 

Herpes simplex viruses A class of double-stranded DNA viruses that infect a particular cell type neurons. Herpes simplex virus type 1 is a common human pathogen that causes cold sores. 

Vaccinia virus is a large double-stranded DNA virus that infects many types of mammalian cells and some invertebrate cells. Its replication cycle is confined to the cytoplasm and can be divided into an early phase and a late phase. The late phase is characterized by the synthesis of structural proteins and enzymes that are packaged into progeny virions. Expression of foreign genes from recombinant vaccinia viruses takes advantage of promoters that are active during the late phase in order to maximize yields of the protein of interest. Several features make the vaccinia virus system... 

Adenoviruses are nonenveloped, double-stranded DNA viruses. There are more than 50 different serotypes of human adenoviruses that have been divided among 6 different subgroups (A-F) based on serologic and... 

Adenovims(es), 64, 65, 172-74, 381, 428-430 attachment receptors of, 476-478 double-stranded DNA viruses and, 172-174 human, 475-476 Adenovirus internalization cell integrins and, 478-482 signaling events and, 481 Adenovirus-mediated endosome disruption, a, integrins and, 482-482 AFM. See Atomic force microscopy (AFM) African horse sickness virus (AHSV), 71 Agrobacterium tumefaciens, 14, 26 AHSV. See African horse sickness virus (AHSV)... 

Double layered particle (DLP), 82 Double-stranded DNA bacteriophage HK97 and, 209-214 large-scale irreversible quaternary structure changes in, 209-214 Double-stranded DNA viruses, 171-178, 243-253... 

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