Cell Genome

Virus particles vary widely in size and shape. As we have stated, some viruses contain RNA, others DNA. We have discussed nucleic acids in previous chapters and have noted that the DNA of the cell genome is in the double-stranded form. Some viruses have double-stranded DNA whereas others have single-stranded DNA (Figure 6.3). 

Some 24 per cent of all gene therapy clinical trials undertaken to date have employed retroviral vectors as gene delivery systems. Retroviruses are enveloped viruses. Their genome consists of ssRNA of approximately 5-8 kb. Upon entry into sensitive cells, the viral RNA is reverse transcribed and eventually yields double-stranded DNA. This subsequently integrates into the host cell genome (Box 14.1). The basic retroviral genome contains a minimum of three structural genes ... 

The ability of such retroviruses to (a) effectively enter various cell types and (b) integrate their genome into the host cell genome in a stable, long-term fashion, made them obvious potential vectors for gene therapy. 

Garaj-Vrhovac, V., D. Horvat, and Z. Koren. 1990. The effect of microwave radiation on the cell genome. Mutat. Res. 243 87-93. 

Nakai, K., and Kanehisa, M. (1992). A knowledge base for predicting protein localization sites in eukaryotic cells. Genomics 14, 897-911. 

A kinase gene has been ddeted from the tumor cell genome. 

A noncompetitive inhibitor has been synthesized in the tumor cells. A kinase gene has been amplified in the tumor cell genome. 

During infection (1), the virus s coating membrane fuses with the target cell s plasma membrane, and the core of the nucleocapsid enters the cytoplasm (2). In the cytoplasm, the viral RNA is initially transcribed into an RNA/DNA hybrid (3) and then into dsDNA (4). Both of these reactions are catalyzed by reverse transcriptase, an enzyme deriving from the virus. The dsDNA formed is integrated into the host cell genome (5), where it can remain in an inactive state for a long time. 

Many viruses and retroviruses have genomes that are single-stranded RNA instead of DNA. These include the acquired immunodeficiency syndrome (AIDS) virus and some retroviruses that cause cancer. Here, an enzyme called reverse transcriptase converts the RNA genome of the virus into the DNA of the host cell genome, thus infecting the host. 

Manipulation of Animal Cell Genomes Provides Information on Chromosome Structure and Gene Expression... 

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