-9- 
the ability to infect a particular host variety which is normally resistant do 
occur in some plant pathogens. I seems desirable, therefore, to add the 
words "or mutation" at the end of prohibition III. 
(c) In view of the newly proposed concept of "novel recombinant DNAs" 
vs. "recombinant DNA" sensu stricto , I wonder whether or not the word "novel" 
should be added between "use of" and "recombinant DNA" in prohibition (iii) 
to improve clarity. 
6) Re-classification of experiments involving ("novel") recombinant 
DNAs from procaryotic plant pathogens in E. coli K12 hosts . The original 
Guidelines recommended the use of P2 + EK1 or P2 + EK2 levels of physical 
and biological containment for the construction of recombinant DNAs from 
procaryotic plant pathogens which normally exchange DNA with E^. col i . Type 
of DNA exchanged was left unspecified. Those that do not, required P3 + EK2 level. 
No distinction between "novel" and "non-novel" recombinant molecules was 
made. These levels were similar to the levels proposed for the cloning of 
DNA from procaryotic human pathogens included in Class 2 of the CDC class- 
ification (e.g. Salmonella, Shigella ). DNA's from plant pathogenic fungi and 
viruses could be cloned in £. col i under P3 + EK2 and P3 + EK1 on P2 + EK2 
respectively. In the current revisions the containment requirements for 
"novel" DNA's from procaryotic pathogens (plant plus human pathogens of CDC 
class 2 that are not known to exchange chromosomal DNA by with £. col i ) have 
been increased to P3 + EK2 levels! 
The reasons for this increase ( 1 or 2 steps) are not clear to me and 
I must express my deep surprise, particularly in view of the following com- 
parisons of proposed containment levels for other plant pathogens: (i) exper- 
iments involving DNA from lower eucaryotes that produce potent n on -polypeptide 
toxins that affect plants (e.g. several plant pathogenic fungi) were lowered by 
[Appendix A — 118] 
