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Vectors For Animals - Animal cells used for transfection(= transformation) may be
(1) tissue culture cell lines,
(2) Xenopus oocytes,
(3) early embryos.(for obtaining transgenic animals), and
(4) even body tissues of individuals (for gene therapy vaccination). DNA fragments from animals are generally cloned in E. coli to obtain sufficient copies for structural analysis.
However, expression of the DNA inserts has to be studied in animal cells; therefore, many of the vectors are shuttle vectors for E. coli and animal cells. The different vectors used in animal cells are derived from viral genomes, and are either

(1) virus like (recombinant DNAs produce virions, i.e., virus particles), or
(2) plasmid-like vectors (these replicate but do not produce virions).
(3) Some other vectors are designed to be unable to replicate.
Another way of looking at animal vectors relates to their ability to replicate in animal cells.
(1) Some vectors are capable of replication (replicating vectors), while
(2) others are not (non-replicating vectors).
Further,
(3) any DNA fragment, or a mixture of fragments can be used to transfect animal cells; these DNA segments become integrated into the cellular genome and express themselves.

In animal cells, vectors that remain and replicate in extrachromosomal state are quickly lost in a few days even when selection conditions favouring their retention are imposed; this is called transient transfection.

But some animal vectors do remain stable in the extrachromosomal state, e.g., those derived from bovine papilloma-virus and those that contain the origin of DNA replication from herpes virus Epstein-Barr. Permanent or stable transfection, however, most often is due to the integration of transfecting DNA into the genome of animal cells; this is also known as insertional transfection.

The DNA integration is usually by nonhomologous recombination, hence in random locations in the genome; this is in contrast to the situation in yeast where recombination is homologous and, as a result, site-specific.

The first animal vector was devised from the primate papova virus, simian virus 40 (SV40). But subsequently, vectors have been developed from many other viruses, e.g., papillomavirus, adenoviruses, the Epstein-Barr herpes virus, vaccinia viruses (all for mammals) and baculoviruses (for insects).

 

 
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