16 
of hearings on the science policy implications of the DNA recombinant 
molecule research issue, the Subcommittee asked selected witnesses to 
provide background information on the biology of this technique. 
B. BASIC BIOLOGY OF THE DNA RECOMBINANT MOLECULE TECHNIQUE 
Dr. Singer 
As pointed out by Maxine Singer, Laboratory of Biochemistry, 
National Cancer Institute, all cellular or cell-like structures which are 
propagated, or which induce propagation, such as viruses, contain the 
chemical information which that cell needs to carry out its various 
functions (unless of course it is defective). In addition to providing 
this information in a precise biochemical form, the cell must also 
possess the ability to turn on and off various segments of this infor- 
mation in response to appropriate stimuli, either internal or external 
to the information center of the cell. Within the last several decades, 
this information center has been subjected to intense study in an 
attempt to describe its structure in precise biochemical terms. This 
has been accomplished and the molecule is now known as deoxyri- 
bonucleic acid or DNA. A great deal is known about this molecule 
and the way that it is duplicated and how information flows from this 
structure to regulate the activities of the cell. However, there is still a 
great deal more that is unknown such as the operational controls or 
“on-off switches” and the change in control systems which produce 
genetic errors. It is the need to characterize the nature of genes, and 
to obtain more precise data about the unknown regulators and dupli- 
cation processes which is producing the pressure to develop and use 
the best techniques available for the study of DNA. DNA recombinant 
molecule research has evolved as the latest and potentially best tech- 
nique now available for use in the research laboratory. 
The DNA recombinant molecule technique was described by Dr. 
Singer. She demonstrated with a simple model the processes involved 
in the cutting of segments from the circular DNA (or plasmid) of a 
bacterium. This process involves the extraction and isolation of the 
DNA molecules (in her example of bacterial plasmids) using a number 
of sophisticated laboratory techniques. The special enzymes are used 
to split the molecule at precise locations and then using other tech- 
niques, the molecule can be rejoined in a similarly precise fashion. If 
a separate fragment of DNA is cut, from a fish for example, it is pos- 
sible to add this unit of fish DNA into the piece of cut bacterial DNA. 
When the bacterial DNA is rejoined it will be a “recombinant mole- 
cule” of bacterial DNA containing the fish DNA. When this recom- 
binant DNA is processed back into a bacterial cell it will be reproduced 
in a normal fashion except that the ^recombinant molecule/’ which 
is the term used to describe the modified plasmid, now will also repli- 
cate the fish segment of DNA within the bacterial cell. Thus, the 
scientist in the laboratory can reproduce in a few hours, because of the 
rapid multiplication time of bacterial cells, a large quantity of the 
portion of fish DNA which was added to the bacterial DNA. This 
portion of new DNA can then be isolated in pure form in large quanti- 
ties for further study. 
An essential factor of DNA recombinant work is the survival and 
replication of the laboratory constructed recombinant molecule when 
[Appendix B — 66] 
