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Present evidence suggests that foreign DNA from bacteria of 
one species, when inserted into bacteria of another species, may 
be expressed in the recipient, depending on the similarities of the 
protein synthesis mechanisms in the two organisms (14). For example, 
if the donor of the foreign DNA produces a toxic substance, then the 
recipient cell may produce such a substance, provided the gene for 
the toxic substance is present in the recombinant. The recipient may 
or may not be more hazardous than the original donor organism, 
depending on the relative ability of the two organisms to grow and 
infect an animal or plant species at risk. 
The evidence available at present is insufficient to predict whether 
or not foreign genes derived from a complex organism (animals, 
plants, yeasts, and fungi) will be expressed in a bacterium in any 
particular instance (14). It may be that specific manipulations will 
be required to permit bacteria to express information from a foreign 
DNA efficiently. Faithful expression of a gene requires accurate 
functioning of the complex bacterial machinery involved in protein 
synthesis. At each step, specific signals originating in the foreign 
gene must be recognized by the bacterial machinery. Evolutionary 
divergence has resulted in different signals in bacteria and complex 
organisms (1 4). 
Attempts to translate animal -virus and animal -cell genes into 
protein, using cell -free systems containing the protein-synthesizing 
machinery isolated from bacteria such as E. coli, yield some protein- 
like products. The protein products characterized to date were not 
faithful to the information in the genes (14). 
In a few cases, intact bacteria containing recombined genes from 
complex organisms have been tested for evidence of expression of the 
inserted gene 0 5, 16). Accurate expression of the genes has not 
yet been demonstrated, although it may occur at a low frequency. 
In some instances, a new protein has been found to replace one 
encoded by a bacterial gene. This result is expected if a bacterial 
gene is interrupted by insertion of the new DNA sequence, and does 
not necessarily indicate expression of the foreign gene. 
DNA fragments from yeast have been inserted into a strain of 
the bacterium E. coli which cannot manufacture the amino acid histidine 
(16). (Histidine - is a component of most proteins and is therefore 
required for the growth of all organisms. ) After insertion, some 
cells no longer required histidine, the need for which had been overcome 
by the yeast DNA. This is the first indication that a foreign gene 
from an organism more complex than bacteria can function in a 
bacterial cell. (Although yeast is a single -cell organism, it contains 
an organized nucleus, like cells of higher organisms. ) 
