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We have learned that in different species analogous genes may be 
organized in different ways and be read off in different directions. 
The existence of diverse and sophisticated control mechanisms for 
turning genes on and off can be inferred. More importantly, the 
chemical structure of these control elements can now be studied. 
Genes corresponding to several important animal proteins have 
been isolated by recombinant DNA techniques. The DNA corresponding 
to the gene for globin, the protein part of hemoglobin, has been cloned 
in an E. coli K-12 system (25). Hemoglobin is the red material that 
transports oxygen in the blood cells. Also the gene for rat insulin 
has been cloned (25). These results will now permit detailed study of 
important features of gene expression and regulation in mammals. 
b . Potential Practical Applications for Medicine, 
Agriculture and Industry. 
Certain of the potential applications will be realized only if the 
reproduction of the recombined foreign DNA in a recipient host cell 
is followed by expression of the genetic information contained in the 
DNA in the form of synthesis of proteins. Since the efficient translation 
of genes of higher organisms (eukaryotes) in bacterial hosts (pro- 
karyotes) has yet to be proved, these potential applications are speculative 
at this time. Applications that depend on the expression of foreign 
prokaryotic genes in prokaryotic recipient cells are presently more 
certain. 
(1) Synthesis of Medically Important Proteins and Other 
Substances ~ 
It has been suggested that eukaryote genes coding for medically 
important substances be attached to bacterial vectors, and that the 
bacteria then be used to produce large quantities of the desired material. 
A number of costly or rare substances would be prime candidates for 
such synthesis: 
• human insulin [A future shortage of animal insulin 
appears likely, and some diabetics are allergic to 
animal insulins. A first step in the realization of 
this goal was recently achieved when the gene for 
rat insulin was successfully cloned in E_. coli (25). ] 
• human growth hormone (presently available only from 
human cadavers and in short supply) 
• clotting factor VIII (for treatment of hemophilia) 
• specific antibodies and antigens (for preventing and 
treating infectious, allergic, and autoimmune disease) 
