STANFORD UNIVERSITY MEDICAL CENTER 
STANFORD, CALIFORNIA 94305 
DEPARTMENT OF BIOCHEMISTRY Area Code 415 
Stanford University School of Medicine 497-G161 
January 10, 1978 
Dr. Donald Fredrickson 
Director 
National Institutes of Health 
Bethesda, Maryland 20014 
Dear Dr. Fredrickson: 
I am writing to urge you to promote the immediate development 
of a bakers' yeast cloning system. Such a system will most likely be- 
come the safest and most versatile of all the cloning systems. 
I was involved in several informal discussions at the 1975 Asilo- 
mar Recombinant DNA Conference and at the 1976 Ban Diego Biohazard 
Assessment Meeting concerning the development of a bakers' yeast 
cloning system. At that time, however, there were a number of techni- 
cal problems that required attention. My laboratory and others have, 
since then, worked on solutions to these problems (i. e. , selective 
marker, DNA transformation system, etc. ). For the most part, they 
have been solved, and I believe a bakers' yeast cloning system can now 
be developed within the next few months. I find this an urgent matter 
since most of my research is becoming totally dependent upon such a 
cloning system. For some experiments we could, however, use trans- 
formed tissue culture cells, although I am reluctant to take this approach 
because I feel it exposes workers in my laboratory to greater risk than 
is necessary. Below, I have outlined some of the advantages and safety 
features inherent in a bakers' yeast cloning system. 
1. The bakers' yeast that would be used ( Saccharomyces cere - 
visiae ) are laboratory strains that have, like E. coli K12, been in cap- 
tivity for several decades. Therefore, many of the properties thatmake 
E. co li K12 a moderately contained strain also apply to bakers' yeast. 
2. Like E. coli K12, none of the laboratory strains of bakers' 
yeast are totally wild type but have various defects that would severely 
cripple them in a completely natural environment. 
3. Unlike E. coli , none of the naturally occurring strains of 
S. cerevisiae are pathogenic to man, animals, plants, or any life form 
(Rose and Harrison, 1969). Furthermore, none of their close relatives 
are pathogenic. 
[Appendix A — 206] 
