Single-Stranded DNA Viruses

Along with the DNA, the virus-encoded J protein also enters the procapsid. What is the role of this protein in assembly/genome encapsidation The J protein, although not necessary for DNA replication. 

Parvoviridae is a family of small icosahedral, nonenveloped animal viruses that contain a linear ssDNA genome of approximately 5000 bases with short unique terminal palindromic sequences that fold back on themselves to form hairpin duplexes (van Regenmortel et al, 2000). They are further classified into two subfamilies, Parvcwirinae and Densovirinae, and various genera depending on host specificity, strand specificity of the genomic ssDNA, and on whether helper viruses are required for productive infection (dependoviruses). Members of the Parvoviridae 

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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). 

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). 

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. 

In 1997 another virus was detected in a Japanese patient with increased transaminases of unknown aetiology. The infectious agent was termed TT virus or TTV, based on the initials of the patient who had been infected as a result of a blood transfusion. (561) This genome is approx. 3,800 nucleotides in length. It is an antisense, circular, single-stranded DNA virus with no outer envelope. There are three conserved open reading frames. The size of the TTV is estimated to be 30-50 nm. It probably belongs to the circoviridae family. (559)... 

Propose how a single-strand DNA virus could replicate by incorporating semiconservative replication into the process. 

Beside chemical risk factors, biological agents also may be responsible for SSc onset. In particular, previous reports analyzed the role played by Citomegalovirus (CMV), a single-stranded DNA virus, as the original epitope of the immune response in SSc, but no clear conclusions have been drawn so far. In fact, it is not clear why such a widespread viral infection by CMV is able to induce SSc only in a small subset of the population. Similar studies were also performed on the analysis of Hepatis B virus, EBV and toxoplasmosis in SSc patients, but no clear conclusion has been obtained so far. ... 

With the exception of single-stranded DNA viruses, DNA occurs as a double-helical (duplex) molecule. In 1953, Watson and Crick constructed a model of DNA compatible with available X-ray diffraction data, chemical data on base composition, knowledge of the three-dimensional structure of nucleotides and the stereochemistry of hydrogen bond formation between different bases. The... 

Other vectors including polio (32), retrovirus (33), bacteria (34), and autonomous parvovirus (35) are all potential oncolytic vectors under development. Autonomous parvovirus is a nonenveloped, single- stranded DNA virus that replicates in cells in the cytoplasm of dividing and nondividing tumor cells. Its envelope can be modified, similar to retroviruses, to contain ligand moieties to target cell surfece receptors. It has been used in vaccine production where it showed low toxicity in human applications (11). Currently, the H-1 strain is being evaluated in the clinic (4). 

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