153 
The suggested changes also reflect the higher risk from potent poly- 
peptide toxins which can be produced by a single gene or cluster of genes, 
as opposed to nonpolypeptide plant toxins such as alkyloids which are end 
products of a complex series of biochemical reactions, and are coded for 
by genes that are not clustered in one region of the DNA. These changes 
are given in lines 16, 17, and 18 of the table. 
Now, the second change relates to the prohibited experiments in Sec- 
tion III, and this is with respect to item number three in the old Guide- 
lines which stated that deliberate creation from plant pathogens of recom- 
binant DNAs that are likely to increase virulence and host range were 
proscribed experiments. It now says that what is proscribed is deliberate 
creation by the use of recombinant DNA of a plant pathogen with increased 
virulence and host range beyond that which occurs by natural genetic ex- 
change. Now, this change is to allow for research to explore the genetic 
controls of virulence and the host range of plant pathogens. For example, 
if we were to generate an avirulent mutant of an organism which is normally 
pathogenic, we could now study the factors necessary for restoration to 
virulence using recombinant DNA techniques. Under the older Guidelines this 
experimentation would not have been allowed, and the Committee felt that 
this was indeed an oversight. 
The third change is one that Dr. Helinski also talked about, and that 
is this restriction on deliberate release into the environment. It was 
thought that eventually — and this is long-term in the future — that some of 
the benefits of recombinant DNA in agriculture will only be realized through 
the eventual release of organisms which have incorporated recombinant DNA. 
So accordingly, we inserted a means for obtaining exceptions to any of the 
prohibitions, of course subject to the recommendations of the Recombinant 
Advisory Committee, and approved by the Director of NIH. 
DR. FREDRICKSON: Are there any questions for Dr. Zaitlin? There are 
two invited witnesses in this area of plants, Dr. Chilton and Dr. Duvick. 
So if you would like to hear them, let us go on. Dr. Chilton, did you 
have some comments you wanted to make? 
DR. 
CHILTON: I 
guess 
not now. 
DR. 
FREDRICKSON: 
Not 
now? 
DR. 
CHILTON: Do 
you 
want me to get up and be 
a witness now? 
DR. 
FREDRICKSON: 
No, 
you can do just as you 
like, but you are 
one of the experts here on plants. 
DR. CHILTON: I would be happy to reply to any questions, but I 
don't have any comments now. 
DR. FREDRICKSON: Is Dr. Duvick here? Dr. Duvick is the Director of 
the Plant Breeding Division of the Pioneer Hi-Bred International, Inc., in 
Johnston, Iowa. 
[ 357 ] 
