46 
One additional level of contained _E^_ coli host-vector systems is de- 
fined and is called EK3. The EK3 systems are essentially similar to these 
EK2 systems, but in order to qualify as EK3, the containment properties of 
EK2 systems must be demonstrated not only by microbiological and genetic 
analysis, but by tests in animals and other relevant environments. EK3 
systems are not presently available. 
May I have the lights, please? 
Having defined the several levels of physical containment, and biolog- 
ical containment, we can now consider the specific recommendations for 
experiments using the E. coli K12 host-vector systems. Each type of experi- 
ment is assigned both a physical containment level, that is a P-level, and 
a biological containment level, that is an EK-level, and the particular 
combination of the two reflects the severity of the estimated potential 
hazard. 
The guidelines are organized for the E^_ coli systems according to the 
source and type of foreign DNA, as outlined in the next slide (8). 
Slide 8 
Experiments with £ coli “Host-Vector" Systems 
Nature of the 'Foreign' DNA 
The sample of DNA containing essentially all the genetic information 
of an organism can be isolated and fragmented by a restriction endonuclease. 
If the entire mixture, containing all the fragments, is used, the experi- 
ment is referred to as a "shotgun," and will call for certain levels of 
containment . 
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