- 2 - 
4. Unlike E. coli , S. cerevisiae is only found to thrive in an 
environment where there is a high sugar content and a low tempera- 
ture (DoCarmo-Sousa, 1969; Yoneyama, 1955, 1956, 1957a, b; and 
Lund, 1954). 
5. Unlike E. coli , there are no viruses of S. cerevisiae . Very 
extensive searches have been made for such viruses. 
6. Unlike E. coli , there are no plasmid-type DNA transfer 
systems in S. cerevisiae . 
7. Because of points 5 and 6, the cloned recombinant DNA of 
S. cerevisiae is very unlikely to be disseminated to other organisms. 
S. cerevisiae is unique in this respect, and in fact, this property has 
been the biggest block to the development of a bakers' yeast cloning 
system. 
8. The products of bakers' yeast are non-toxic. In addition to 
being a major ingredient of health foods, it is also found in bread, 
cake, and other baked goods, as well as in beer, wine ar d other drinks. 
The above points illustrate that a bakers' yeast cloning system 
is likely to be the safest possible approach. It is inconceivable that 
yeast can be dangerous. We have been ingesting large amounts of 
yeast and yeast products for more than 10, 000 years. 
On the following page, I have listed some references you might 
find useful. 
Sincerely yours, 

Ronald W. Davis 
Associate Professor of Biochemistry 
RWD/lh 
[Appendix A — 207] 
