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Slide 17 
Presently Useful Eukaryotic Vectors 
'foreign' DNA 
Polyoma Virus 
normal host: mice 
infects humans: NO 
oncogenic in small newborn mammal 
'transforms' mammalian cells 
Simian Virus 40 
normal host: monkeys 
infects humans: YES 
oncogenic in small newborn mammals 
'transforms' mammalian cells 
Because Simian Virus 40 infects human beings, and also because Simian 
Virus 40 and related viruses have been isolated in connection with several 
human disease states, the proposed guidelines assume that polyoma affords 
the higher level of biological containment, and therefore more stringent 
physical containment of Simian Virus 40 is required than for polyoma. 
An increase in the level of biological containment afforded by the 
two unaltered viral DNAs can also be obtained. This is shown on the next 
slide (18). 
The guidelines require that the viral DNA used for recombination with 
a foreign DNA must itself be defective. Such defective viruses are unable 
to reproduce efficiently. They are available and they result from changes 
or mutations in the viral DNA. A defect is indicated schematically here by 
an X in the circular DNA of the virus. Upon infecting a cell, no new viral 
particles can be made. For the purpose of an experiment which requires the 
production of viral DNA, infection is carried out in the presence of a 
helper virus, which supplies the genes for the missing function. 
As shown in the next set here, this could be another defective which 
is defective for another gene somewhere else on the DNA, and between these 
two viral genomes, all the necessary genes are provided, and two types of 
viral particles can be produced containing either of the two original defec- 
tive genomes. Or, as shown in the next line, an intact form of the defec- 
tive gene might previously have been inserted into the chromosomal DNA of 
the recipient cell, thus also supplying the missing function and permitting 
the production of the desired defective virus. 
[196] 
