vector containing the foreign DNA may leave the original K12 host cell and 
enter another E. coli cell, perhaps one of the related strains normally 
found in humans. 
41 
As you have already heard this morning, the extra chromosomal elements 
that will be used as vectors can be transferred from one cell to another 
during mating. Therefore, in estimating the containment of the recombined 
DNA itself, we need to discuss this transfer process and the likelihood that 
it will occur. 
May I have the next slide (4), please? 
Slide 4 
£ coli Plasmids as Vectors 
Nonconjugative plasmids: 
Conjugative plasmids: 
But: 
A B 
A B 
B C 
B C 
As Dr. Berg pointed out, two kinds of extra chromosomal elements can 
be used as vectors in E_j_ coli K12 systems. This particular slide deals with 
plasmids. They are shown here as small circles, and the chromosomal DNA is 
represented in each case by the egg-shaped structure. 
Certain plasmids are called nonconjugative because, as shown here, they 
are unable to be transferred from one cell to another, as indicated by the 
X here. Because of this they would not be able to leave the original K12 
cell were it to enter the alimentary tract. For this reason the guidelines 
recommend the use of nonconjugative plasmids as vectors in recombinant 
research. 
[182] 
