April 30, ±y/b 
the original host or as a consequence of transmission of the 
vector and/or elened DNA fragment by transformation, transduction 
or conjugation to a host with properties common to those in the 
natural environment." 
g 
Pg. 21. "For EK2 phage vectors , no more than one in 10 
reeembinant phage partielea should be able to perpetuate itself 
and/or a the cloned DNA fragment under non-permissive conditions 
designed to represent the natural environment either (a) as a 
prophage or plasmid in the laboratory host used for phage propagation 
or (b) by surviving in natural environments and transferring itself 
and/or a the cloned DNA fragment to a host (or its resident lambdoid 
prophage) with properties common to those in the natural environment." 
The new wording differs very significantly from the older form by its 
de-emphasis of measurements related to the propagation of the cloned DNA 
yet these are the only really meaningful measurements. The wording of the older 
form seems to us better, but whatever wording is ultimately used it ought to 
stress that the cloned segment is the element of concern. 
2) We urge that before any proposed host/vector system is accepted as 
safely meeting the guidelines, for example for EK2, the proposers of the system 
should make their primary data available for public scrutiny, either by publication 
in a journal or by distribution in the NARSM circular. In this way, reviewing 
bodies who certify safer vectors would know that the relevant data had been 
sufficiently available for public criticism before certification was completed. 
Sincerely 
Oliver Smithies 
Leon J. Cole Professor of Genetics 
and Medical Genetics 
Frederick R. Blattner 
Assistant Professor of Genetics 
Harvey E. Eaber 
Post-Doctoral Fellow 
OS : fm 
xc: P. Leder; W. J. Gartland 
[ 536 ] 
