the University of rllabama in Birmingham / university station / Birmingham, alabama 35294 
the Medical Center /department of microbiology / October 27, 1978 
Dr. Donald S. Fredrickson 
Director 
National Institutes of Health 
Bethesda, Maryland 20014 
Dear Don: 
I just returned from attending the sixth course on Biohazard Containment and 
Control for Recombinant DNA Molecules which was held at the Frederick Cancer 
Research Center and where I participated as one of the course lecturers. At 
this meeting, I learned that you received numerous comments concerning the 
containment requirements for cloning primate, mammalian and avian DNAs in £. 
coli K- 12 host-vector systems; more specifically, that P3 + EK1 be allowed as 
an alternative to P2 + EK2. I was also informed that this question has been 
referred to the Recombinant DNA Advisory Committee, which is meeting in 
Frederick next week. In my letter to you of September 23, 1978, I specifically 
made no comments about the required levels of containment for the above- 
mentioned types of experiments, since I wholeheartedly concurred with the 
reasons for not allowing the option of P3 + EK1 in lieu of P2 + EK2. Therefore, 
the purpose of this letter is to indicate the reasons for my support for main- 
taining the P2 + EK2 containment levels as now stipulated in the proposed re- 
vised Guidelines. 
Two objections have been made to the use of EK2 host-vector systems. One of 
these concerns the limited number of EK2 systems available and the other con- 
cerns the ease with which these systems can be used. The first objection is 
very real and my laboratory group is endeavoring to remedy this situation. 
Nevertheless, a diversity of EK2 systems with different mutational defects in 
host strains is much more necessary when cloning DNA from prokaryotic and 
lower eukaryotic organisms, where it is possible to select for expression of 
donor DNA sequences that specify a product to complement a genetic defect in 
the host strain than when cloning DNA from mammalian and avian sources since 
it is quite dubious that any gene function from higher organisms will be 
functionally expressed to complement a genetic defect of a prokaryotic host. 
On the other hand, there is a need for a greater diversity of cloning vectors 
to facilitate selection for functional expression of higher eukaryotic DNA 
sequences. These cloning vectors are being constructed in a number of 
laboratories and obtaining approval for their use with existing E^. coli K-12 
host strains is a much simpler task than constructing and obtaining approval of 
an entire host-vector system. This is particularly true when the vector is a 
modification of an already approved vector such as pBR322. It is thus my opinion 
that this first objection to the lack of diversity of EK2 host-vector systems is 
not an important argument to support the option of P3 + EK1 in lieu of P2 + EK2 
AN AFFIRMATIVE ACTION / EQUAL OPPORTUNITY EMPLOYER 
[A— 446 ] 
