Dr. Donald S. Fredrickson 
Page Five 
E . Experiments with Eukaryotic Host-Vectors 
1. Any comments I make regarding the use of SV40 DNA as a 
cloning vector could be construed as self-serving; therefore, I'm wary 
about proceeding. But let me try. Work with SV40 virus, its DNA and 
the respective defective forms (those being generated naturally during 
infections or constructed enzymatically in vitro ) are now done in P2 or 
P3 facilities depending upon the concerns of the investigator. (There is 
no NIH guidance or requirements on this matter. ) Defective genomes 
cannot multiply without helpers, consequently, if they escape they can 
infect cells only if they are coinfected with a complementing virus. I 
have given quite a bit of thought to making hybrids in which prokaryote 
DNA segments are introduced into the SV40 DNA molecule in place of 
specifically excised segments of the viral DNA. I have been unable to 
conjure up data or a substantive reason to support a ban on such experi- 
ments or even to require that they be done in P4 facilities. It's interest- 
ing to note that not a single person thought that introducing bacterial genes 
into SV40 and thence into animal cells was potentially hazardous when we 
made the first such hybrid three years ago. What has changed since then? 
Only the level of scrutiny. Do not misunderstand: I agree that using SV40 
DNA as a vector to clone random segments of mammalian or primate DNA 
provokes considerable concern (such experiments do require P4 facilities 
according to the guidelines) but I do not feel it is outrageous to perform 
experiments with prokaryote DNA inserts under P3 conditions. 
However, I can see where dealing with emotional concerns is im- 
portant to get things moving and, therefore, I would support, without 
conviction, a requirement for P4 conditions to carry out such cloning ex- 
periments. It is likely, I believe, to force people to switch to polyoma 
DNA as the vector and that may be safer in the long run. 
I'd like to illustrate, however, how research could change things. 
For example, certain modifications in experimental design could permit 
considerably safer experimentation with SV40; we have recently isolated 
the origin of SV40 DNA replication (this consists of 500-600 base pairs of 
the genome total of 5000 but this could very likely be reduced to about 100 
base pairs) and planned to use that origin segment as a vector to clone 
"foreign" DNA segments. In this way only that portion of the SV40 DNA 
chromosome would be involved in the cloning. Depending upon the size 
and "packageability" of such DNA recombinants, it could provide the safest 
eukaryotic vector available. My point is that we cannot shut off the oppor- 
tunity for innovation through experimentation. 
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