Animal Viruses -

Viral DNA is an obvious candidate for use as a vector for the introduction of foreign DNA into animal cells because so much is known about the life cycles of the viruses and their entry into and exit from animal cells further, depending on the cells they infect, they may either replicate to give progeny or integrate their DNA into host chromosomes.

With viral infection it is possible to ensure that each recipient cell has many copies of the foreign gene. And since the viral genome includes strong promoters, it is possible to ensure efficient expression of foreign genes inserted into the viral DNA.

Different kinds of animal viruses, such as simian virus 40, bovine papilloma virus, retrovirus, etc., are useful as vectors for gene cloning in animals.