LABORATORY OF GENETICS 
406 Genetics Building 
Madison, Wisconsin 53706 
O. Smithies 
Office: (608) 262-2976 
Laboratory: (608) 262-104 
April 30, 1976 
Dr. Donald S. Frederickson 
Office of the Director 
N.I.H. 
9000 Rockville Pike 
Bethesda, Maryland 20014 
Dear Dr. Frederickson: 
Several of us at the University of Wisconsin-Madison are working in the 
field of DNA cloning. Two matters in the latest version of the proposed 
guidelines (available to us in April, 1976) are of concern to us since they 
appear to depart significantly from the proposed guidelines (January, 1976) 
emanating from the Torrey Pines meeting. 
1) We understand that the wording of parts of the guidelines proposed in 
January as they relate to the Biological Containment Criteria Using E. coli 
K12 Host-vectors may be changed as indicated here:- 
* 
Pg. 18. " EK2 host-vectors - these are host-vector systems that 
have been genetically constructed and shown to provide a high level 
of biological containment as demonstrated by data from suitable 
tests performed in the laboratory. The genetic modifications of 
the E. coli K-12 host and/or the plasmid or phage vector should 
not permit survival of the elened a genetic marker carried on the 
vector j preferably on the inserted DNA fragment in other than 
specially designed and carefully regulated laboratory environments 
at a frequency greater than 10~ . This absolute measure of 
biological containment has been selected because it is a realistic 
measurably entity. Indeed, by testing the contributions of pre- 
exisiting and newly introduced genetic properties of vectors and 
hosts, individually or in various combinations, it should be 
possible to substantially indicate, if not prove, that the specially 
designed host-vector system can provide a margin of biological 
containment in excess of that required . 
g 
For EK2 plasmid vectors , no more than one in 10 host cells 
eenfeaining a ehimerie plasmid should be able to perpetuate the 
Vector and/or a cloned DNA fragment under nonpermissive conditions 
designed to represent the natural environment either by survival of 
* . 
-Qld-versien new versvon 
[ 535 ] 
