17 
it is reintroduced back into a cell system. For the purpose of the 
Federal guidelines which are now in effect to regulate, DNA recom- 
binant molecule research is defined as: 
* * * molecules that consist of different segments of DNA which have been 
joined together in cell-free systems, and which have the capacity to infect and 
replicate in some host cell, either autonomously or as an integrated part of the 
host’s genome. 
The discoveries which were crucial to the recombinant molecule 
technique were the identification of the very special enzymes which 
permit the “cutting” of the molecules and the development of tech- 
niques to collect the small recombinant molecules and reintroduce 
them into a living cell so that they will replicate. 
C. ALTERNATIVE TECHNIQUES 
In her discussion of the technique of DNA recombinant molecule 
research, Dr. Singer indicated thtft there are several alternative 
techniques available. These include the standard microbiological 
techniques which have been used in the study of bacteria for decades— 
studies of mutations, deliberate induction of mutations with radiation 
or chemicals, selection of natural antibiotic resistant forms, natural 
viral transfer of genetic properties, work with sexual inheritance, and 
similar classic studies in bacterial genetics. These types of studies 
have been very fruitful in the single celled bacteria but similar de- 
tailed studies have not been possible in higher organisms. In fact, it is 
because of the great detail available on the genetics of the single celled 
bacteria E. coli that this organism has been the principal subject of 
work with the DNA recombinant molecule technique. 
Dr. Singer pointed out that direct synthesis of a gene also was a 
new possibility for certain kinds of work; however, she emphasized 
that the major difficulty with this technique is the enormous complex- 
ity of the work and the amount of time to complete the synthesis (the 
most recent work required about nine years for one gene). Although 
such work does reiquire considerable time, she considers this factor as 
the least important impediment to synthesis as a technique. The struc- 
ture of the gene must be known before the synthesis can take place and 
she emphasized that the DNA recombinant molecule technique is 
the only practical method at this time for precise definition of structure 
of any number of genes, and particularly- the genes of higher organisms. 
The alternative to direct synthesis of genes is to use an intermediate 
synthetic technique in which the biochemical cell messenger (messen- 
ger RNA) for the construction of a particular protein is isolated 
and then used as a copying template by the researcher. Dr. Singer 
summarized the disadvantages of this method as including the 
current difficulty with isolation of the pure messenger substance 
(the RNA) and the fact that the control switches related to DNA 
activity are hot amenable to examination. 
Dr. Lewis 
Among the alternative techniques of particular interest* Charles 
Lewis, Staff Scientist, Agricultural Research Service, identified fusion 
of a single cell from each of two plants — a non-sexual hybridization — 
which is accomplished in the laboratory. This is another technique by 
[Appendix B — 67] 
