Virus reproduction

Viruses are classified initially on the basis of the hosts they infect. Thus we have animal viruses, plant viruses, and bacterial viruses. Bacterial viruses, sometimes called bacteriophages (or phage for short, from the Greek phago meaning to eat), have been studied primarily as convenient model systems for research on the molecular biology and genetics of virus reproduction. Many of the basic concepts of... 

Because viruses only replicate inside living cells, research on viruses requires use of appropriate hosts. For the study of bacterial viruses, pure cultures are used either in liquid or on semi-solid (agar) medium. Because bacteria are so easy to culture, it is quite easy to study bacterial viruses and this is why such detailed knowledge of bacterial virus reproduction is available. 

The temperate virus does not exist in its mature, infectious state inside the cell, but rather in a latent form, called the provirus or prophage state. In considering virulent viruses we learned that the DNA of the virulent virus contains information for the synthesis of a number of enzymes and other proteins essential to virus reproduction. The prophage of the temperate virus carries similar information, but in the lysogenic cell this information remains dormant because the expression of the virus genes is blocked through the action of a specific repressor coded for by the virus. As a result of a genetic switch, the repressor is inactivated, virus reproduction occurs, the cell lyses, and virus particles are released. 

Piotrovskii LB, Kozeletskaia KN, Medvedeva NA et al. (2001) Effect of fullerene C60-polyvinylpyrrolidone complexes on influenza virus reproduction. Voprosy Virusologii. 46(3) 38—42 (Russian). 

The virus uses the apparatus of the host cell to reproduce itself, i.e., the host cell is fooled into reproducing the virus. Reproduction of the virus, requiring the synthesis of its nucleic acid and protein overcoat, proceeds differently depending on whether the virus contains DNA or RNA. DNA viruses are reproduced by the host cell using its enzymes and building blocks (nucleotides and amino acids) in the same manner that the host replicates its own DNA and directs its own protein synthesis. 

Ans. A reovirus is a double-stranded RNA virus. Reproduction involves RNA replicase as in the case of single-stranded RNA viruses. 

The most studied aspect of phytoalexin elicitation is that generated by fungal pathogens of plants. Karban et al.[22] found induced resistance and interspecific competition between spider mites and a vascular wilt fungus. McIntyre et al. [2A] demonstrated that 7 days after tobacco plants were infected with tobacco mosaic virus, reproduction of the green peach aphid, Myzus persicae, was significantly reduced on these infected plants. Inoculation of plants with tobacco mosaic virus induced resistance to several pathogens, however the mechanism for induced resistance was not characterized. 

Feldman M Ya, Zalmanson ES, Mikhailova LN (1971) Mechanism of action of products of reactions of formaldehyde with nucleotides (methylene bis-dinucleotides) on the cell and virus reproduction (in Russian). Mol Biol 5 847-857... 

Genty, N., and Bussereau, F., 1980, Is cytoskeleton involved in vesicular stomatitis virus reproduction J. Virol. 34 777. 

Host-virus relationships. 2. Pathology, Cellular. 3. Viruses —Reproduction. I. Series. 

Just as the bacteriophage system serves as a model of virus reproduction, it may be taken as an example of protein synthesis. For this it has the advantages of the net autocatalytic production of a specific nucleoprotein with biological activity and well-defined physical properties. 

There are several concepts, more closely related to ideas of virus reproduction than to those of protein synthesis, which are not supported... 

The role of the 6S fraction of RNA in virus reproduction has not yet been explained. Kelly and co-workers consider that this component is perhaps an adaptation for replication of a specific part of the virus genome. 

After penetrating into bacterial cells the DNA of this phage undergoes the typical fate which we saw for RNA in cases of virus reproduction considered above it is replicated by complementary synthesis with the preliminary formation of double-stranded DNA. This process was discovered in later experiments (Sinsheimer, 1961 Sinsheimer et al., 1962) by fractionation of nitrogen- and phosphorus-labeled DNA of infected cells in a density gradient of cesium chloride at various times after infection. This double-stranded form of phage DNA was called the replicative form (RF). 

As we have seen in the case of virus polycistronic RNA templates, despite their integral structure, they produce different proteins in sharply different amounts. Each cistron of such a template functions at its own intensity and different cistrons produce different numbers of molecules per unit time depending on the amount of them required for virus reproduction. In this situation it is easier to assume that each cistron is not functionally connected with each other, but works independently at its own individual speed. 

Regulation of the velocity of synthesis of expedient proteins in the necessary proportions for virus reproduction, which may be determined by variations in the half-life of different messenger RNA fractions resulting in different concentrations of these fractions at the site of synthesis and by a system of modulator codons for regulating protein synthesis at the template level. 

Despite the fact that the introduction of one unit of a virus within a living cell of a susceptible host is followed by the production of millions of virus units, almost nothing is known about the reproductive process. It seemed possible that preparation and isolation of tobacco mosaic virus containing radioactive phosphorus and inoculation of this virus into the diseased plants with the subsequent extensive multiplication of the virus should provide some information concerning the process of virus reproduction. This line of thought induced Stanley (169) to investigate the radioactivity of Turkish tobacco plants inoculated with labeled tobacco virus. Similar investigations were also carried out by Born and associates (25). 

---