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Analogous issues must be considered for the case in which animal 
viruses are the carriers of foreign DNA. Many viruses are simply 
described as DNA molecules enclosed and protected by coats of protein 
molecules (12,13). The protein coat protects the DNA from environmental 
effects, thus increasing the ability of the viral DNA to infect a cell. If 
viral DNAs are recombined with foreign DNAs in such a way that 
necessary viral genes remain intact, then the recombinant DNA may in 
turn be able to produce, and be packaged in, the coat of the virus. 
Inadvertent dispersal of such a viral particle outside of the laboratory 
might then result in entry of the recombinant DNA into cells of living 
organisms. The foreign genes may be expressed, resulting in the 
formation of a protein foreign to the infected cell, or the uncontrolled 
synthesis of a normal protein. The likelihood of expression of the 
foreign genes will probably depend on the degree of relatedness 
between its source and the infected organism (3 4) as well as its location 
in the viral DNA used as vector. Currently, few relevant experimental 
data are available (4). 
(2) The recombined DNA may itself cause pathogenic 
or toxic effects' ~ ™ 
Foreign DNA inserted in a bacterial gene might so alter the 
microbial cell's properties that it becomes harmful to other organisms. 
This might happen, for example, through a change in the growth 
rate and competitive advantage of the recipient microbial cell, resulting 
in increased virulence of a mildly pathogenic bacteria. In general, 
one would expect the inserted DNA to result in a reduced growth 
rate and a selective disadvantage to the organism, as discussed 
in IV-C-l-a above. Similar issues arise where animal viruses serve 
as carriers of foreign DNA. 
It is also necessary to consider situations in which DNA molecules 
themselves may escape from the laboratory or from the experimental 
host cell and enter cells of living organisms with which they come 
in contact. Although free DNA molecules are themselves relatively 
fragile (and the probability that they would survive, in a significant 
form or for a significant time, in air, water, or any other medium, 
is considered remote), they can be protected in nature in a variety 
of ways and be released either into, or close to, a living cell. 
When a cell or virus dies, or comes close to or invades the 
tissue of another living organism, the recombinant DNA may 
effectively enter a new cell. A hazardous situation similar to that 
described above might ensue if foreign proteins were manufactured 
in this "secondary" recipient. The recombinant DNA might survive as 
an independent cellular component, or it could recombine by natural 
process with the DNA of the secondary recipient. Various possible 
deleterious consequences of such a recombination may be considered. 
