page 3 
mobilization is generally simpler and easier to perform than transformation which 
requires prior isolation of the DNA molecules .Mobil ization tests are also essen- 
tial during vector construction experiments. In effect, this provision creates a 
dilemma. In the proposed revisions, in which self-cloning using indigenous plas- 
mids will be excluded from regulation, the recombinant DNA can be mobilized out 
of the host strain into other procaryotes. On the other hand, DNA cloned from 
the same donor procaryotes into a different recipient procaryote cannot be mobilized 
by a conjugative plasmid back into the original donor, despite the fact that the 
latter will be receiving its own DNA by this procedure. 
If the "exchanger" list is based on plasmid exchange these arguments are 
irrelevant. However, if the list is based on chromosomal DNA exchange the pre- 
sent wording in the definition of HV-1 systems will turn out to be very restrictive 
and unreasonable in view of the proposed deregulation of self-cloning. Since the 
P + HV containment levels assigned under the Guidelines are presumably commensurate 
with the probability that the cloning host may be converted into a pathogen, it is 
the secondary biohazards (runaway plasmids) that must be compared. Differences in 
the escape potential of recombinant plasmids from various unmodified (HV-1) gram- 
negative procaryotic primary cloning hosts, although habitat-dependent, can only 
be judged in very hypothetical general terms. 
If a narrow definition of exchangers is adopted I suggest that allowance be 
made for conjugative mobilization in HV-1 systems when the DNAs are of procaryotic 
origin, either by changing the HV-1 definition or in some other appropriate fashion. 
For example, the level of physical containment could be increased one step. Alter- 
natively, conditional suppressor-dependent conjugative plasmids could be used 
when the ultimate recipient does not contain a suppressor gene. Finally, a conju- 
gative plasmid unable to replicate or establish itself in the ultimate recipient 
could be employed. 
I hope that you and the Committee members give these matters adequate consi- 
deration. 
Sincerely yours, 
- y ■ 
Nick Panopoulos 
Assistant Plant Pathologist, Lecturer 
Copies forwarded to: 
E.D. Adelberg 
A. Campell 
P.R. Day 
S . Falkow 
W.H. Gartland 
S.K. Gottesman 
D. R. Helinski 
R.B. Hornek 
L. Jacobs 
E. K1 utter 
J.W. Littlefield 
J.K. Settlow 
J. Spi z izen 
E.S. Redford 
W.P. Roe 
D. Stetten 
L. Walters 
M. Zaitlin 
Coptic 
[Appendix A — 281] 
