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The proposed revisions in the experimental section of the Guidelines 
are of several types, and given the limited amount of time, I would like 
to select just a few of what we view as the major revisions for comment. 
Again, at the outset I should note that several categories of experiments 
have not been formally changed as to their physical and/or biological con- 
tainment levels. However, it should be emphasized, in view of the more 
vigorous criteria for EK2 and EK3 host-vector systems as described by Dr. 
Gottesman, the containment levels for these experiments that haven't been 
revised have effectively been made more stringent. 
Several categories of experiments are classified at a lower containment 
level in the proposed revisions. For example, the cloning of mammalian DNA 
other than primate DNA has been reduced a single step in containment level — 
that is, from P3 plus EK2 in the present Guidelines, to P2 plus EK2 in the 
proposed revisions. 
Another example is the single-step reduction of the containment levels 
for the cloning of primate DNA. That reduction is from P4 plus EK2 to P4 
plus EKl. That is one of the options in that particular category of experi- 
ments. 
A major consideration in these proposed one-step reductions in contain- 
ment levels is our increased confidence as a Committee in the biological 
containment and safety of the EKl and EK2 host-vector systems. I will 
attempt to elaborate on the basis for this increased confidence in these 
systems in a few minutes, although a number of the points have already been 
raised earlier today. 
Another type of proposed revision in the experimental section that 
should be noted is the deletion of certain classes of experiments, and 
primarily this involves those experiments which are concerned with DNA 
from prokaryotes that naturally exchange DNA with E . col i . These deletions 
have been proposed by our Committee on the basis of their exclusion if the 
proposed redefinition of the Guidelines to include only novel recombinant 
DNA is adopted. I want to emphasize, however, that the majority of the 
categories of experiments have not been deleted, but in fact in certain 
cases have been extensively broken down into more specific categories that 
have been assigned containment levels. One case in particular is the cate- 
gory dealing with the cloning of animal viruses. Dr. Wally Rowe will follow 
me and make further comments on revisions in this category. 
I stated earlier that the proposed lowering of containment levels in 
certain categories of experiments has as a major basis our increased confi- 
dence in the use of E^ col i K-12 in the form of EKl and EK2 systems as a 
host for recombinant DNA experimentation. I want to elaborate on this 
st atement . 
Given the central role of E. col i K-12 in recombinant DNA research 
at the present time, our Committee has been actively soliciting information 
and new experimental data pertaining to the biological properties of this 
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