4 . 
jffhis "disarmed" host has not been constructed at this time (11/1/75), at least no paper 
ii 
’describing it has been published. DNA from various organisms and viruses is being 
cloned in E_. col i at this time in hosts chosen by the individual investigator. 
|These hosts, insofar as we can find out, do not carry a variety of non-revertiblc, 
independently acting mutations which give the host the low-survival, lowered genetic 
■ B 
.’exchange properties of the theoretical "disarmed host." It is essential that the 
[December meeting of the guidelines committee specify one E_. col i strain as the "safe" 
. 
E. col i host, to be used in all experiments, and make it available. This "December 
'75 disarmed host" will probably be far short of the theoretical ideal "disarmed" 
E. col i and can and should be replaced with superior strains as they are constructed. 
It is important that there be at any one time one specific "disarmed" £. col i strain 
available and used in all cases. Similarly the December meeting can specify the 
specific "safest" E_. col i vectors available and to be used: one mutant lambda vector, 
one pSClOl vector, etc. This will aid uniformity of precautions on the part of all 
investigators. However, we do not wish to see continuing for a long time a process 
of replacing the December '75 "disarmed" E_. col i hosts and "disarmed" £. col i vectors 
with more "disarmed", later model E_. col i host-vectors. Rather, we feel that the 
E. col i system is inherently of such potential hazard that it should be rapidly 
phased out of use for recombinant DNA experiments. 
In as much as E. col i is a normal resident of the human intestine, pharynx, 
and a human pathogen, its choice as a recipient organism for implanting foreign 
genes seems reckless. VI i t h its universal, intimate relation with humans, E^. coJj_ 
presents a fundamental ecological unsuitability for recombinant DNA experiments. 
On the other hand, knowledge of E^. col i molecular genetics is far more advanced 
than that of any other organism, offering the theoretical possibility of 
containment via genetic construction of crippled E. col i hosts and vectors. We 
[ 355 ] 
