65 
First slide, please. 
Slide 1 
GOALS IN CONSTRUCTING SAFER E_. CPU K-12 
Strains should possess nutations that: 
1. Increase usefulness of strains for research 
2. Preclude colonization of and survival in intestinal tract 
3. Preclude biosynthesis of cell wall in non- 1 aboratory 
controlled environments 
k. Lead to degradation of DNA in non- 1 aboratory controlled 
env i ronmen t s 
5. Cause cloning vector replication to be dependent on host 
6. Preclude or minimize transmission of recombinant ONA to 
other bacteria 
7. Permit monitoring of strain 
Our goals in constructing safer Ej_ coli K12 stipulated that strains 
should possess mutations that: one, increase their usefulness for the re- 
search; two, preclude colonization of and survival in the intestinal tract; 
three, preclude biosynthesis of cell wall in non-laboratory-controlled en- 
vironments; four, lead to degradation of DNA, that is, genetic information, 
in non-laboratory-controlled environments; five, cause cloning vector repli- 
cation to be dependent on the host; six, preclude or minimize transmission 
of recombinant DNA to other bacteria; and seven, permit monitoring of the 
strain. 
We have now constructed and tested a strain which meets these specifi- 
cations except for that stipulated in goal five, since development of safer 
cloning vectors is being worked on by other researchers. 
The next slide (2) gives a description of our potential EK2 host. 
Strain xl776, and its derivative, xl876, which carries the pSClOl plasmid 
cloning vector, possess the following traits: first, mutations conferring 
important properties are due to deletions in genetic information, thus they 
are stable; two, they require diaminopimelic acid, an unusual amino acid 
not prevalent in nature, which is needed for cell wall biosynthesis, and 
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