42 
Another type of plasmid shown here by a squiggly circle is call conjuga- 
tive since it can be transferred to another cell, and the use of conjugative 
plasmids is therefore discouraged. However, the situation is somewhat more 
complicated as shown in the group of reactions at the bottom of the slide. 
Cell A contains a conjugative, that is a squiggly plasmid, and can 
transfer it to Cell B, which in this case already contains a nonconjugative 
plasmid, so that Cell B winds up with both types of plasmids. The presence 
of the conjugative plasmid gives Cell B now the ability to transfer not only 
the conjugative plasmid but the nonconjugative one as well to a third Cell, 
C. Cell C might be one of the E. coli types normally residing in the bowel, 
and therefore the use of a nonconjugative plasmid does not totally assure 
containment of the recombinant. 
In order to evaluate a particular plasmid-E. coli combination as to 
containment, we need to ask the likelihood that this series of reactions 
will occur. While we are missing some relevant information, what data are 
available suggest that the probability can be quite low, depending on the 
particular nonconjugative plasmid that is used. 
With certain known and useful plasmids, the entire series of events 
shown on the bottom of the slide occurs at frequencies that are less than 
one in 10 9 — that is, one in one thousand million. This is the first time I 
have used this terminology, but it occurs throughout the guidelines. For 
those of you who are unfamiliar with it, I have summarized it on the board. 
The number 10 9 is a one followed by nine zeroes. The number 10® is a one 
followed by eight zeroes. It is just much easier to use this terminology, 
so that as I use it, and if I forget to tell you exactly what it is in more 
straightforward terms, you can look at this. 
Okay, so the events involving the transfers that I showed you at the 
bottom of the slide appear to occur at frequencies that are less than one in 
10 9 or one in one thousand million, and in fact they are usually undetect- 
able under laboratory conditions designed to resemble natural conditions. 
Host-vector systems made up of E_^_ coli K12 and such plasmids therefore 
appear to have only very limited ability to spread recombinant DNA molecules. 
Now, viruses that infect coli , which are called bacteriophage, are 
another source of DNA that is useful for recombinant DNA experiments. Some 
relevant properties of bacteriophage are summarized on the next slide (5). 
Bacteriophage particles which are shown here are made up of small 
protein molecules surrounding a DNA molecule, which is shown here as the 
squiggly line. The genes characteristic of the bacteriophage are in this 
DNA, and it is to this vector that a foreign DNA might be joined. The 
bacteriophage particle or the DNA can enter a sensitive Ej;_ coli K12 cell 
and one of three things can happen. 
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